Okay, I noticed that no change at all in the SQL DB had an effect ... And I know why: I deleted the config.ini and selfoss managed to create a sql-lite.db itself.

Well, okay then ... But I highly recommend changing the update description:

1. Delete all old files excapt for the folder data AND THE FILE CONFIG.INI
2. Upload all except for folder data
3. GIVE WRITING RIGHTS TO THE PUBLIC FOLDER AGAIN