Ok, I fixed the problem.
It had nothing to do with the database.
Maybe something went wrong during installation.
the folder clearbits was missing in:
JONAS_4_7_6/work/webapps/jonas/LibreSource-Community-2.2/LibreSource-Web-2.0/pages/images
I copied it from the LibreSource-Web-Static-2.0 folder.
Now it works