Hello Gunnar H.,

I think, the configuration database may corrupted.
You can try to delete the dcf-Files, but I do not
know, if it would help in this case.

see FAQ:
"How do you delete the DCF file of your WinCC project?"

https://support.industry.siemens.com/cs/de/en/view/109763043

If this would not help, you should create a Servicerequest
and send the project to the Technical Support of Siemens
for checking the database.

Regards

Georg Berghof