It seems that the mariadb database got damaged when upgrading. The same effect happened then on win and android kodi (not able to set content and crash when playing any file). The db got upgraded with osmc tho. It did display an upgrade page on the first restart, and I did get MyVideos119.
Fortunately I have all watched states backed up with trakt.tv so I just created a new database and now it works.
After I “set content” of my sources, it just does not get saved. All other settings seem to stay. The scan also never starts.
All video files I tried to play (via file section) crashes the system (sad face). I’m using a NFS share.
The skin changing problem got solved with just trying a lot of times. After the 20. try of confirming the change skin dialogue it suddenly stayed. This issue is very strange.