System.InvalidOperationException: There is an error in XML document (0, 0).

[gromett]

After some experimentation, I could get it working by deleting migration.xml and system.xml.

If one would like to fix this problem too, he can try deleting only these so that configs aren't lost unnecessarily.

Thank you very much.   Worked great for me.

For reference: On a debian system they are in /etc/jellyfin/