Error message after upgrade to 12.0.0


I just have upgraded from 11.0.3 to 12.0.0

Since the update i get the following error message:

`Error	no app in context	OCP\AppFramework\QueryException: Could not resolve OCA\Richdocuments\Settings\Section! Class OCA\Richdocuments\Settings\Section does not exist`

My research ended in the resolution that this is usually related to a miss configured Collabora installation.
But i did not install or configure it at all. Neither before the update nore after.

I hope anyone can help because this error is coming very frequent.

Thanks a lot
Best regards

Nextcloud version : 12.0.0
Operating system and version : Ubuntu 16.04.2 LTS