404 when fetching cover
When importing music via server-dir (or when trying to fix album covers of already imported tracks) I sometimes got a 404 ([Album 7750] cannot fetch cover from musicbrainz: caused by: HTTP Error 404: NOT FOUND).
This is an album for which it happened: https://musicbrainz.org/release/f7409045-932c-4fdd-9544-77bd9a504dca
The album has a cover on MB, so I think it normally should be found.