For now everything is working again for some reason after multiple restarts of the rPi. I still got errors in the log, but it works. I don’t dare to do any changes (like changing back to 2.3 release) until I have a full afternoon to fix likely errors/restore backup.
Usually after a change (upgrade, disconnecting the controller in order to go include new things, restart of the pi…) some of my things lose their Lifeline and I have to figure out which ones and go edit them. So it’s always a little bit of trouble haha.