No controller error when starting program

We experience occasionally that the UR has the “NO CONTROLLER” error when pressing play on a program in the teach pendant. The program contains an event from our own URCap. This has happened on two different robots around twice a month, when they are used every day for development.

I can provide a support file if it can help.

Steps to reproduce:
This is an occasional bug that we cannot reproduce on purpose.

Expected Behavior:
When pressing the play button, that the program starts as usual.

Actual Behavior:
When pressing the play button, the UR goes to “NO CONTROLLER” state without any visible error message.

Robot Serial Number:

Affected Version(s):
Polyscove version
UR robot: UR16e