Mhhh,
so checked the json file within the jsondb folder - but found at least no formatting or EoF issue. Syntax via Notepad++ and Samba checked, later on stored with Nano.
Then I restored a backup (of those files) from last week - but also no change/ success.
I also cleared the cache multiple times by now, forgot to mention this yesterday. But no change. Dashboard and anything related stays dead, Grafana is ok (so its related to OH)