Known issues

Known for firmware 2020.0 LTS on all supported PLCnext Control devices:

If you use the Linux command scp without the option -p to copy configuration files from a Linux PC to the directory /opt/plcnext/projects on the controller, the file permissions are partly set incorrectly.

Remedy: After copying the configuration files, use the Linux command chmod to set the file permissions in such a way that the firmware can delete the configuration files in case of Download Changes (group: plcnext, owner: plcnext_firmware).

Known for firmware 2020.0 LTS and 2020.3 on all supported PLCnext Control devices:

The length of the password is limited to 64 bytes, and the length of the user name is limited to 128 bytes. Note that the entered characters are UTF-8 encoded, i.e. one character can occupy up to four bytes (e.g. umlauts).

Therefore, if using UTF-8 special characters (Unicode) for the user name and password, the length restriction (user name = 64 bytes, password = 128 bytes) can take effect, although the maximum character length was not used. The reason is that the number of bytes and not the number of characters is limited in the RSC service.

Known for firmware 2020.3 and 2020.6 on all supported PLCnext Control devices:

If the controller is rebooted using the Linux command sudo reboot or by means of the RSC service IDeviceControlService::RestartDevice(), a system watchdog may occur in rare cases. Because the RSC service is also used by the Reboot button in the PLCnext Engineer cockpit, it can also occur after using that button. As a consequence only a Cold Start is possible when the controller is subsequently booted, so all retain variables are reinitialized.

This behavior does not occur when the operating voltage is switched off and the controller is then booted.

Known from firmware 2020.3 to 2021.6 on all supported PLCnext Control devices:

The system watchdog is not yet active during the startup phase if you start C++ extensions very early. If the user code causes a crash during this phase, this can lead to an endless boot loop. You can solve the problem by removing the SD card before rebooting.

Known for firmware 2020.6 or newer on all supported PLCnext Control devices:

Setting local time zones is not fully supported. After setting a local time zone, unexpected results may occur when reading out times from different contexts (RTC-S FB, OPC UA®, SPNS LOG).

Known for firmware 2020.0 LTS or newer on all supported PLCnext Control devices:

If a firmware 2020.0 LTS or newer is downgraded to 2019.9 or older and then upgraded again to firmware version 2020.0 LTS or newer, a Cold Restart is performed. The retain variables are set to their default values.

Known for firmware 2021.0 LTS on all supported PLCnext Control devices:

Coming from 1.x or 2019.x firmware, the 2021.0 LTS firmware update removes the following files that are not edited by PLCnext Engineer nor are they intended to be modified by the user:

• /opt/plcnext/projects/Default/Plc/Eclr/Default.eclr.config 
• /opt/plcnext/projects/Default/Plc/Gds/Default.gds.config 
• /opt/plcnext/projects/Default/Plc/Meta/Default.meta.config 
• /opt/plcnext/projects/Default/Plc/Plm/Plm.config 
• /opt/plcnext/projects/Default/Plc/Esm/Default.esm.config 
• /opt/plcnext/projects/Default/Plc/Esm/ServiceTask.esm.config 
• /opt/plcnext/projects/Default/Plc/Esm/Globals.esm.config 

Known for firmware 2021.0 LTS or newer on all supported PLCnext Control devices:

If the PLCnext system firmware has not started up properly, the WBM displays the error message "Bad Gateway 502".

Known for firmware 2021.6 or newer on all supported PLCnext Control devices:

If a user component causes a crash before the system watchdog is activated the firmware terminates and the controller is available via SSH only. (Note: The system watchdog is activated just before the IControllerComponent::Start() method is invoked.)

Known for firmware 2021.6 or newer on AXC F 3152:

Reset to default setting type 2 can only be performed with a running Linux system. If a user makes changes in the Overlay File System (overlayFS) that lead to problems booting the system, then resetting the device via the reset button is not possible.  

Only known workaround: Boot the controller with an external SD card, copy the overlayFS to this external SD card and delete the overlayFS on the controller after that.

Known for all firmware releases previous to 2022.0 LTS on all PLCnext Control devices

Changes made as the Linux® root user (such as manual changes in configuration files) can cause problems when updating the firmware to release 2022.0 LTS. In this case the controller has to be reset to default settings (type 1) before updating the firmware successfully.

The reason for this issues is that changes made by the Linux root user are stored in the upperdir folder of the Overlay File System (overlayFS). If a new firmware release brings along changes in the same files, those firmware changes cannot become active due to the previous changes in the upperdir folder.

Note: Even Linux® commands like adduser or addgroup cause changes of their corresponding configuration files in the overlayFS.

Known for firmware 2022.0 LTS or newer on AXC F 1152 and AXC F 2152:

An attempt to set the system time of the controller to a timepoint in year 2038 or later results in a system watchdog. This issue will be fixed in a future firmware release. For this the Linux kernel must be updated (the update is currently planned for firmware version 2024.0 LTS).

Known from firmware 2022.6 on all supported PLCnext Control devices 

If a firmware version < 2021.0 LTS  of a controller is updated to a higher version, the WBM of the controller is no longer accessible. The WBM is only accessible again after the controller has been restarted one more time.

This behavior has been rectified in the next firmware release for the regarding devices:

• 2022.6.2 hotfix for RFC 4072S
• 2022.9 release for AXC F 2152
• 2023.0 LTS release for AXC F 1152 and AXC F 3152

Known for all firmware versions on RFC 4072S and BPC 9102S:

LIC SD cards are only supported from firmware release 2022.6 or newer.  If you're using a LIC SD card with an RFC 4072S or BPC 9102S and performing a reset to default settings type 2, then the firmware version of the delivery state that is reactivated might not support the LIC SD card type. Because for these controllers an SD card is mandatory, updating the firmware by means of the usual update procedure via the WBM to a firmware version ≥2022.6 that supports the LIC SD card is no longer possible then. In this case, proceed as follows:

• Connect to the controller via an SFTP client, e.g. by means of WinSCP (see Connecting to the controller).
• Upload a firmware container of a version ≥2022.6 to /var/volatile/tmp. This folder is located in the RAM of the controller and has about 4 GB of free memory.
• Perform an update with the following command via SSH console:
  rauc install /var/volatile/tmp/<updatecontainer>.raucb
  ↪ The update is executed and the LIC SD card will be active on restart.

Known for firmware 2020.0 LTS to  2021.0 LTS on all supported PLCnext Control devices:

The DBG LED or touch panel indicator should signal if a variable has been set via forcing in debug mode in the PLC project. This behavior is currently not supported: Despite forcing the variable the DBG LED or touch panel indicator remains off.

Known for firmware 2020.3 on RFC 4072S:

The removal of the fan during operation is not detected correctly due to a technical feature.

Known for firmware 2020.6 on AXC F 3152 and RFC 4072S:

If the SD card is removed during operation and then the supply voltage is disconnected, the device will operate with the internal voltage buffer until it is discharged. This can take up to 30 seconds.

Known for firmware 2021.0 LTS or newer on AXC F 1152 and AXC F 2152:

The Link and the Active LEDs on the X1 and X2 network interfaces are not illuminated when a 10BaseT connection is used.

Known for firmware 2021.6 on AXC F 1152 and AXC F 2152:

In rare cases, the controller may no longer recognize the SD card after an interruption of the power supply. All LEDs flash and the controller cannot be connected via Ethernet. Only some 2 GB SD cards are affected by this. 

Known for firmware 2020.6 or newer on all supported PLCnext Control devices:

DHCP can only be activated for Ethernet adapters that are not assigned as PROFINET controllers or PROFINET devices. To make the settings effective in the network, the device must be restarted.

Known for firmware 2020.6 on all supported PLCnext Control devices, and persisting from firmware 2021.0 LTS or newer in the touch panel of RFC 4072S:

In general, when DHCP is switched on, the current IP settings are not yet displayed in the WBM or on the touch display, but the static settings last set are displayed.

Known for firmware 2020.6 and 2021.0 LTS on RFC 4072S, and on AXC F 2152 and AXC F 3152 if used in combination with an AXC F XT ETH 1TX extension module:

If there are several Default Gateway settings, only the setting of LAN1 is used for all LAN adapters. Different settings of other LAN adapters (i.e. for LAN2) are ignored.

Known for firmware 2020.6 and 2021.0 LTS on AXC F 2152 with AXC F XT ETH 1TX attached:

If both network adapters in the PLCnext Control and the extension are configured with the same subnet, then the PROFINET Controller functionality will not work as desired. A proper connection setup is not possible with this configuration.

Known from firmware 2023.6 on AXC F 1152 and AXC F 2152:

Under high network load the built-in Ethernet interface of the affected PLC types sometimes can reach a blocking state. In this state only a power reset can re-enable the interface communication. To avoid this the PLCnext Technology network driver has a mechanism implemented to detect such situations and to react with a reset of the specific interface. By default behavior of the Linux network stack a predefined default gateway configuration gets lost during this reset.
Note: The Ethernet interface of the AXC F XT ETH 1TX is not affected. 

Known for firmware 2021.9 on AXC F 2152 and AXC F 3152 with AXC F XT PB attached:

If a PROFIBUS station is missing after successful first commissioning, this is not indicated via the system variables or the diagnostic interface. Only the status LED on the AXC F XT PB extension module indicates this problem.

Known for firmware 2021.9 on AXC F 2152 and AXC F 3152 with AXC F XT PB attached:

The EXT LED on the controller incorrectly lights up red instead of green if the PROFIBUS left alignment is connected correctly. However, this does not affect the function of the left alignment.

Known for firmware 2021.9 or newer on AXC F 2152 and AXC F 3152 with AXC F XT PB attached:

If a faulty PROFIBUS configuration is set after successful first commissioning, this is not displayed via the system variables or the diagnostic interface. The affected PROFIBUS station is not commissioned, but is displayed as ready.

Known for firmware 2021.9 or newer on AXC F 2152 and AXC F 3152 with AXC F XT PB attached:

The acyclic PROFIBUS communication DPV1 is not yet supported.

Known for firmware 2020.0 LTS and 2020.3 on all supported PLCnext Control devices:

The PROFINET connection setup can take a long time in combination with a very large PROFINET structure.

Known for firmware 2020.0 LTS to 2020.6 on all supported PLCnext Control devices:

Frequent calls of PROFINET Read Record and Write Record function blocks may disturb the communication to the corresponding AR. A connection termination may occur.

Known for firmware 2020.3 on AXC F 1152 and AXC F 2152:

After switching off MRP, a restart of the PLCnext Control is required in order for it to work properly.

Known for firmware 2020.3 and 2020.6 on all supported PLCnext Control devices:

If firmware 2020.3.1 or 2020.6 is downgraded to an older version, the PROFINET name is lost.

Known from firmware 2021.0 LTS to 2022.3 on all supported PLCnext Control devices:

A PROFINET device connection may be terminated and re-established if cyclic tasks at all ESM cores are used, and if these tasks have an execution duration longer than the configured monitor time of a PROFINET device. 

• Check the execution duration in your code, set by usingESM_DATA.ESM_INFOS[..].TASK_INFOS[..].MAX_EXEC_DURATION.
• Compare to the monitor time set with PLCnext Engineer in the PLANT area → Interface node → Settings tab → Monitor time.

Known for firmware 2021.0 LTS or newer on AXC F 1152 and AXC F 2152:

The use of a PROFINET cycle time of 1 ms leads to a deviation of the jitter behavior required by the controller certification. Operation in  this state is possible but not recommended.

Known for firmware 2021.6 or newer on AXC F 2152, AXC F 3152, and RFC 4072S:

PROFINET PRL (Phoenix Redundancy Layer) is not supported. Firmware release 2021.0 LTS was the last release supporting PRL, newer releases do not support this feature.

Known for firmware release 2022.6 or 2022.9 on all supported PLCnext Control devices:

If a PROFINET Device indicates a module difference (ModuleDiffBlock) without corresponding submodule differences, this module difference is not reported in the related notification. This behavior has been observed with PROFINET Devices from other vendors than Phoenix Contact.

Additionally this module difference is not shown in the Diagnostics - PROFINET WBM page nor can it be retrieved via RSC IArConfigurationService, or via the IEC 61131-3 function block GET_MODULE_DIFF_BLOCK.

Known for firmware release 2023.0 LTS and 2024.0 LTS on RFC 4072R:

In the Diagnostics → Profinet WBM page, the Overview tab fails to update the status of the PROFINET controller. The Profinet Controller Function is indicated as Deactivated even if the PROFINET controller is active and operating its connected PROFINET devices. Nevertheless, in the Device List and Tree View tabs the status is indicated correctly. Will be fixed in soon.

Known from firmware release 2024.6 on all supported PLCnext Control devices:

The PROFINET controller stack had to be adapted to the increased requirements of the PROFINET certification test, resulting in an increased CPU load in ESM 1. In exceptional cases, this can lead to a task watchdog in PLC projects with many PROFINET connections and tightly set ESM task watchdog times.

Known from firmware release 2024.6 on all supported PLCnext Control devices:

If the PROFINET controller is deactivated when a device with more than one network interface is initialized for the first time, the name of the PROFINET controller interface moves to the name of the PROFINET device interface. However, a new assignment of the correct name  by the user after this shift is then permanently adopted.

Known for firmware 2020.3 and 2020.6 on all supported AXC F x152 stations containing an Axioline Smart Elements backplane:

If an Axioline bus contains a power terminal and a Smart Elements module with empty slots, the bus will not restart after a power failure.

Known from firmware 2021.6 on AXC F 1152, AXC F 2152 and AXC F 3152:

Some Axioline modules (e.g. analog outputs) provide status information in their process data. In case of a module error (e.g. loss of power supply) these process data inputs are filled with an error code. However, in certain situations these process data inputs return 0 instead of the error code. 
Only process data inputs of modules connected to the controller's local bus are affected. Not affected are retrieving module errors via PDI request as well as displaying these errors at the WBM page Diagnostics - Local Bus.

Known for all firmware versions on all supported PLCnext Control devices:

If the firewall is activated via WBM, the operation of EtherNet/IP™ is no longer possible. This can be remedied by subsequently activating the ports:

• Incoming connections: port 44818
• Outgoing connections: port 2222

Known for firmware 2020.0 LTS on RFC 4072S:

After downloading a safety-related project, a new connection to PLCnext Engineer is sporadically not possible. The following error message is displayed: "Error during login! A communication error was detected".

Known for firmware 2020.0 LTS on all supported PLCnext Control devices, and for firmware 2020.3 on AXC F 3152:

If you initiate a warm start in PLCnext Engineer and this is not possible internally, a cold start is performed automatically, i.e., the retain variables are reinitialized.

Known for all supported firmware releases on RFC 4072S:

When two instances of PLCnext Engineer simultaneously log on to the same SPLC, a failsafe state of the SPLC may occasionally occur. The error messages „0x115A“ and then „0x8041“ are displayed on the SPLC.

Known for firmware 2020.0 LTS or newer on all supported PLCnext Control devices:

During a PLCnext Engineer program download (both total and "changes only"), the web server returns a 503 error ("busy") for requests to the HMI pages.

Known for firmware 2020.0 LTS and 2020.3 on AXC F 1152, AXC F 2152, and RFC 4072S:

After debugging a PLCnext Engineer project with breakpoints the project may stop immediately after restarting.

Known for firmware 2020.3 and 2020.6 on all supported PLCnext Control devices:

When debugging IEC 61131 code with activated breakpoints, display errors may occur in the call sequence function and variable contents.

Known for firmware 2020.3 or newer on all supported PLCnext Control devices:

The content of these system variables is permanently set to 0:

• ESM_DATA.ESM_INFOS[*].TICK_COUNT
• ESM_DATA.ESM_INFOS[*].TICK_INTERVAL

However, if a request for this system variable is made from a REST client, the HMI server does not return the value of that system variable (which is always zero), but instead it returns a different value that looks like a tick count.

Known for firmware 2020.3 to 2023.3 on all supported PLCnext Control devices:

Sporadically a PLCnext Engineer project may reject the Download changes command without giving a reason. This issue is solved with firmware release 2023.6.

Known for firmware 2020.6 on all supported AXC F x152 devices:

A task watchdog may sporadically occur with a low-priority PLC task with a cycle time in the range of seconds if the running PLC project is being stopped and immediately restarted with a cold/warm/hot start.

Known from firmware 2020.6 or newer on all supported PLCnext Control devices:

If Event, EventTask, ServiceTask or Globals is used as the name of a task in a user program then an error condition of the controller occurs when downloading the project to the controller. This is because these class names are already used internally.

Known for firmware 2021.6 and 2021.9 on all supported PLCnext Control devices:

Sporadic communication errors may occur between PLCnext Engineer and the controller.
Remedy: Reboot the controller.
This issue is resolved with firmware release 2022.6.

Known for firmware 2022.0 LTS (initial release) on AXC F 1152 and AXC F 2152:

Depending on the history of firmware releases installed on a particular PLC it can happen that after updating to firmware 2022.0 LTS a web browser can no longer connect to the PLCnext Engineer HMI at the PLC. As remedy the PLC needs to be reset to default settings (type 1). This issue has been fixed with the 2022.0.4 LTS hotfix.

Known for firmware 2022.0 LTS on RFC 4072S:

Used and free data memory for an IEC 61131-3 application is not displayed correctly in PLCnext Engineer. With the 2022.6 release, this issue is resolved.

Known for firmware 2023.0.0 LTS and 2023.0.1 LTS on AXC F 1152 and AXC F 2152:

If the PLC rejects a Download changes command (Write and Start Project Changes executed by PLCnext Engineer), e.g. because the change cannot be performed in real time, the PLC is rebooted due to a system watchdog.

Known for firmware 2020.6 and 2021.0 LTS on all supported PLCnext Control devices:

When a Solution App is uninstalled by the PLCnext Store, it can happen that the controller then no longer reacts to any actions by the PLCnext Store, although it reports the statusonline. A system watchdog was also sporadically observed. This behavior has not been observed when using the offline deactivation in the WBM for uninstalling a solution app.

Known from firmware 2020.6 to 2022.9 on all supported PLCnext Control devices:

Sporadically it can happen that a restart of the firmware requested by an app installation does not work properly. If the firmware does not start up correctly, the controller can be restarted by one of the following possible actions:

• Restart of the firmware via SSH (/etc/init.d/plcnext restart)
• Reboot of the controller via SSH
• Power reset of the controller

Known for firmware 2021.9 or newer on all supported PLCnext Control devices:

Licence operations, such as adding or removing a licence, include cryptographic operations and hence shall only be performed if the PLC is stopped. This may avoid side effects due to preempting the license operations by tasks running with higher priority.

Known for firmware 2020.6 on AXC F 2152:

After resetting the controller there is no TrustStore with the name „proficloudv3“. The TrustStore is necessary for the update via Proficloud.

Workaround: Re-create the TrustStore in the WBM on the controller.

Known for firmware 2023.0 LTS on all supported PLCnext Control devices:

If the Proficloud V3 connection is activated via the Proficloud WBM page or after the installation process of an app directly from the PLCnext Store (online installation) the generation of a keypair (i.e. for a certificate) is not possible anymore. Thus, it is not possible to create a new Identity Store with a autogenerated keypair.

It is still possible to create a new Identity Store by uploading a keypair as .pem file or via pasting the keypair as text. Also, establishing a connection to the PLC via PLCnext Engineer or WBM or SSH is still possible. Defective Identity Stores can be easily deleted via WBM.

To be able to create a new Identity Store with an autogenerated keypair again, do this:

Scenario A:  Proficloud V3 connection has not been disabled but an app was installed via the PLCnext Store

•  Reboot the device.

Scenario B:  Proficloud V3 connection is enabled via the Proficloud WBM page

• Disable the Proficloud connection and reboot the device.

Known from firmware 2022.9 to 2023.3 on all supported PLCnext Control devices:

When Proficloud is configured to cache values (WBM setting Remanent Buffering Enabled) and when the connection between PLC and Proficloud is broken, the consumed memory increases. If this situation continues for a too long period, it may even lead to a System Watchdog. This issue has been fixed with firmware version 2023.6 und and hotfix 2023.0.7 LTS.

Known for firmware 2020.0 LTS on RFC 4072S:

If a task with priority 0 is created on ESM2, a prolonged cycle of the safety project may occur. For this reason, select a priority >0 for a task on ESM2.

Known for firmware 2020.0 LTS to 2021.0 LTS on all supported PLCnext Control devices:

The PLCnext CLI must be used with an SDK for the same release. Downward compatibility throughout releases cannot be guaranteed. From the 2021.6 release the PLCnext CLI comes as a separate file. See the Tool downloads overview for compatible releases, and PLCnext CLI for procedures with newer firmware releases.

Known up to firmware 2020.0 LTS on all supported PLCnext Control devices:

C++ projects that were created using WorkerThread in SDK release 2019.0 LTS have to be compiled again using an SDK version ≥ 2019.3. Otherwise, the WorkerThread is not loaded after restart of the application.

Known from firmware 2020.0 LTS to 2022.0 LTS (initial release) on AXC F 1152, AXC F 2152, and AXC F 3152:

An ESM event task could be executed only up to 2,147,483,648 times (1,024³x2) after power on. This affected mainly the Interbus cycle end ESM event task. This task is available for the AXC F controllers in combination with AXC F IL ADAPT or  AXC F XT IB extension modules.
This issue has been solved with the 2022.0.5 LTS hotfix.

Known for firmware 2020.3 on all supported PLCnext Control devices:

With the GNU compiler types GCC (8.3.0, 9.2.1) used, a quadratic increase in compilation time and memory consumption on the desktop PC is observed when very large structures are used. Note this behavior if you use a large number of ports in PLCnext Technology applications (e.g. connection of a very large number of Simulink® signals).

Known for firmware 2020.6 on all supported AXC F x152 devices:

A task watchdog may sporadically occur with a low-priority PLC task with a cycle time in the range of seconds if the running PLC project is being stopped and immediately restarted with a cold/warm/hot start.

Known from firmware 2020.6 or newer on all supported PLCnext Control devices:

If Event, EventTask, ServiceTask or Globals is used as the name of a task in a user program then an error condition of the controller occurs when downloading the project to the controller. This is because these class names are already used internally.

Known for firmware 2021.6 on all supported AXC F x152 devices:

If a fieldbus I/O of data type Bitstring or OctetString is connected to a program port of data type ARRAY, only the value of the first ARRAY element is transferred. The remaining elements are not copied.

Known for firmware 2021.6 and 2021.9 on all supported PLCnext Control devices:

If the socket of the classes Arp::System::Commons::Ipc::IpcSocket, Arp::System::Commons::Net::Socket, and Arp::System::Commons::Net::TlsSocket is shut down, the Select() method returns true. Compared to BSD sockets, this behavior is unexpected. As this is a legacy method it is now remarked as deprecated. With firmware version 2022.0 LTS and newer the Poll() method is implemented.

Known for firmware 2021.6 or newer on all supported PLCnext Control devices:

With the SDK version 2021.6 the language standard C++ 17 has been set in the compiler options (-std=c++17). The firmware itself is also compiled with this option set. Besides some general C++ issues related to this C++17 standard, the following issue is related to PLCnext Technology:
C++ 17 introduces the data type std::byte which is unfortunately not compatible with Arp::byte. Therefore, if the namespaces std and Arp are both active the compilation, this results in an error. In this case existing C++ sources have to be adjusted so that they explicitly use Arp::byte (e.g. by adding using byte = Arp::byte;).

Known from firmware 2023.0 LTS to 2023.3 on all supported PLCnext Control devices:

When a MQTT client function block of the IEC 61131-3 IIOT_Library_V4.x is used and the connection to the MQTT server is broken, a System Watchdog occurs after several reconnection attempts. This issue has been fixed with firmware version 2023.6 und and hotfix 2023.0.7 LTS.

Known from firmware 2024.0.0 LTS to 2024.0.3 on all supported PLCnext Control devices:

Writing process data to a fieldbus via the ANSI C API does not work. This issue has been fixed with the 2024.0.4 LTS hotfix.

Known for firmware 2024.6 on AXC F 1152, AXC F 2152, and AXC F 3152:

With firmware version 2024.6, an unnoticed binary change occurred in the class Arp::System::Commons::Ipc::IpcSocket by accident. Consequently, code which uses this class and which has been compiled with an SDK of firmware version 2024.0 or older will not work with firmware version 2024.6.0 or 2024.6.1. For use with these firmware versions the code needs to be re-compiled with the SDK version 2024.6.

Known for all firmware releases on all supported PLCnext Control devices:

After a system watchdog, only a cold start can be performed when the controller is started. The retain variables are set to their respective initialization values.

Known for firmware 2020.0 LTS or newer on all supported PLCnext Control devices:

If a firmware 2020.0 LTS or newer is downgraded to 2019.9 or older and then upgraded again to firmware version 2020.0 LTS or newer, a Cold Restart is performed. The retain variables are set to their default values.

Known for firmware 2020.3 or newer on all supported PLCnext Control devices:

If a requested warm start is not possible to execute via PLCnext Engineer, an implicit Cold Restart is automatically executed. The retain variables are set to their initialization value. From firmware 2021.0 LTS, a dedicated state of the retain values can be restored from a backup.

Known for firmware 2020.0 LTS to 2020.6 on all supported PLCnext Control devices:

With extended retain handling in the context of this firmware, the retain variables are reinitialized by a cold start when downgrading to firmware 2020.3 or older. A previous saving of the retain variables by the user is not supported with firmware version 2020.6 or older.

Known for firmware 2020.0 LTS or newer on all supported PLCnext Control devices:

Using the maximum quantity structures of the retain data can increase the task duration of the using task. This can trigger a task watchdog for time-critical applications.

Known for firmware version 2024.0 LTS on AXC F 2152 with left-aligned SPLC 1000 or SPLC 3000

If a standard variable in PLCnext Engineer is assigned to a safety variable and a standard variable, then the standard variable is not written. This issue will be fixed a.s.a.p.

Known for firmware 2020.0 LTS on all supported PLCnext Control devices, and for firmware 2020.3 on AXC F 3152:

If the use of preexisting C++ applications (Function Extensions) results in mixed operation of the OpenSSL versions 1.0.2 and 1.1.1, the controller does not boot.

Recommended: If you are using an app of the type "Function Extension" from the PLCnext Store, check whether an update is available in the PLCnext Store.

Known for firmware 2020.3 on AXC F 1152, AXC F 2152, and RFC 4072S:

For security reasons, applications should no longer be linked against the outdated OpenSSL version 1.0.2.

Known for firmware 2020.3 on AXC F 1152, AXC F 2152, and RFC 4072S:

Updating the OpenSSL version 1.0.2 to version 1.1.1 can lead to problems with existing C++ applications that are based on this and run in the same process (e.g. function extensions). In the event of incompatibility, the firmware may not start up.

Recommened: If you are using an app of the type "Function Extension" from the PLCnext Store, check whether an update is available in the PLCnext Store.

Known for firmware 2020.3 or newer on all supported PLCnext Control devices:

Access to long STRING variables outside the application is limited to 511 bytes. This concerns reading and writing via the RSC services IDataAccessService and ISubscriptionService. These services are used by OPC UA®, PLCnext Engineer HMI and the online functions of PLCnext Engineer, among others.

The same applies for WString variables (available from firmware 2021.6). Please note that WString variables are converted to UTF8 when accessed via RSC services.

Known for firmware 2020.6 on all supported PLCnext Control devices:

In the IDeviceStatusService RSC service, the Status.Memory.Usage.Percent parameter no longer returns a value with the following user roles:

• Engineer
• Commissioner
• Service
• DataViewer
• DataChanger
• Viewer
• UserManager

Known up to firmware version 2024.0 LTS on ALL PLCnext devices

If the REST ReadVariables command is used with POST then the JSON object created from the content is not deleted properly and causes a system watchdog due to the memory leak. This issue will be fixed a.s.a.p.; meanwhile, use the GET flavor of that ReadVariables command. This issue has been fixed with firmware version 2024.0.3 LTS.

Known for firmware 2020.3, 2020.6 and 2021.0 LTS on all supported PLCnext Control devices:

Due to changes of the OPC UA® server namespace, some OPC UA® clients may cause a BadNodeIdUnkown error. The affected OPC UA® clients do not synchronize the namespaces correctly on start-up, resulting in invalid NodeIds; e.g. Visu+ <= v2.54 throwing an -2143420416 error code. 

Visu+ users updating from firmware 2020.0 LTS or 2021.0 LTS are not affected, but updating to or from a feature release (a non-LTS release) will cause this issue.

Remedy: Visu+ users can adjust the namespaces manually as described in this Phoenix Contact Knowledge Base article. User of other affected OPC UA® clients should contact the respective manufacturer.

Known for firmware 2021.0 LTS or newer on all supported PLCnext Control devices:

Starting with firmware 2021.0 LTS, the application URI is checked against the client side certificate. Some clients do not support the application URI so the OPC UA® Server declines a connection; e.g. Visu+ ≤ v2.54 throwing an -2145976320 error code. This issue only comes up when using a PLCnext Engineer template ≥ 2021.0 LTS.

Remedy: Checking the application URI can be disabled in the OPC UA® Server configuration as shown in this Phoenix Contact Knowledge Base article.

Known from firmware 2023.0 LTS to 2023.3 on all supported PLCnext Control devices:

If subscribing to multiple matrices within a single subscription the OPC UA Server does not provide data. However, if only one matrix is subscribed, it works.
If a 2D matrix of type String is subscribed, the variable update of a previously subscribed 2D Int matrix freezes. This condition can only be removed by resubscribing to the 2D Int matrix.

Known from firmware 2023.0 LTS to 2023.3 on all supported PLCnext Control devices:

If a matrix for monitoring is used, various unexpected results occur when using "IndexRange" and "String" as data type:

• When initially reading out the matrix after logging in, a "DataChange" event with several changes is erroneously triggered.
• If a "DataChange" event is performed after writing, the strings in the matrix are truncated.
• Sporadically a Segmentation Fault occurs when reading out the matrix.

For now, OPC UA Server rejects client requests with that specific combination to prevent crashes.

Known from firmware 2023.0 LTS to 2024.0 LTS on all supported PLCnext Control devices:

Very sporadically a SIGSEGV (segmentation fault) could occur which leads to a system watchdog. The stack trace in the Output.log file indicated that one or more methods of the class Arp::Services::OpcUAServer::Internal::InformationModel::Common::SampleGroup are involved. In many cases this error occurred when variables have been removed from or added to the list of monitored items, where in parallel other clients created or freed OPC UA sessions. The longer the list of monitored items, the more likely it is that the error will occur.
This issue has been fixed with the 2024.0.4 LTS hotfix.

Known for firmware 2023.0 LTS on AXC F 1152 and AXC F 2152

Using the value 0 as NamespaceIndex in the configuration of OPC UA client may lead to a fatal error.
This issue has been fixed with the 2023.0.2 LTS hotfix.

Known from firmware 2023.0 LTS on all supported PLCnext Control devices:

The OPC UA® client feature relies on changes in the source data to trigger the transfer of data between the client and the server. If the source data does not change for any period of time, then there is no guarantee that the data values will be synchronised between the client and the server, for example after an interruption in the client-server connection. 

Known for firmware 2024.6 on all supported PLCnext Control devices:

Invalid and changing input data can occur in the event of a Modbus exception. This error will be fixed with a further firmware release. Meanwhile, as a workaround, process the read data only if the TCP communication is active and no exception is reported. That is true if the STATE variable has the value 16#0001.

Known for firmware 2020.0 LTS or newer on all supported PLCnext Control devices:

If two or more DataLogger sessions are configured to write to the same database, only the data of one session will be transferred to the database on the SD card at the end. The user does not receive a message that not all data can be saved.