+Update,
the datastore is a 'drive me crazy' element.
The UTF convert process stopped at 14%, because it had an issue with converting Tapatalk tables.
As I dont need TT, I decided to remove all tables. Started the coverting processes again. Same problem after 14% was reached, Tapatalk was mentioned again as reason.
I followed Stuarts recommendation and cleaned the datastore - hey and voila, It worked as well