Basically I started from scratch. I removed MB docker via docker page, then deleted its app data.
I then reinstalled from community apps. Make a copy of your musicbrainz token as a precaution, but your docker template should still have info from previous install.
I had issues with current latest version of Picard, 2.1.3 (even after fixing MB docker), so I rolled back to 2.1 I happen to still have and it doesn't crash anymore.