Cant shutdown ursim

I cant shutdown the ursim GUI. When I try to close the application, i get the following error message in the terminal:

11:17:21.689 WARN  - Unknown shutdown sequence initiated {thread: Thread-8 , loggerClass: com.ur.polyscope.system.impl.internal.ShutdownServiceImpl$1}
java.lang.Throwable
	at com.ur.polyscope.system.impl.internal.ShutdownServiceImpl$1.run(ShutdownServiceImpl.java:40) [polyscope-system-impl-6.5.14.jar:?]
2021-05-31 11:17:21,758 FATAL Unable to register shutdown hook because JVM is shutting down.

when i type

pkill ursim 

the process is killed, but the GUI is still open.
When i remove my URCap, the Problem not there anymore.

The URCap starts no Thread.
What could cause this problem?

I tried several other URCaps. The Problem only accurse, if any URCap is installed.

I think your urcap will have some problems, causing the GUI to freeze. I think you can open ursim through the terminal command line, such as ./start-ursim.sh, so you can force Ursim to be closed by Ctrl+C. It is easier to debug, and there should be no GUI stuck phenomenon

Pressing Ctlr + C in the Terminal dont have any impact.

If i start a new URCap process, the older application will not close - it opens another window and starts a new ursim .
The only way i found to close ursim is to kill the java process in the system monitor.
This happens on ursim 5.9 and 5.10