Comment by sippeangelo

I wrongly assumed I was below version 10.10.7 and tried to "upgrade" to it first as the migration guide said, but this completely blew up and the db migrations failed. I then tried to skip straight to 12 and that also crashed on startup during db migrations, so I just nuked the whole Jellyfin config and started from scratch.

Bit unfortunate how this can even happen, but it's on me for not checking or taking a backup first. The config/db really contain anything important anyways, other than "watched" markers that are already out of sync for me across Emby/Jellyfin/Plex.