Update: I’m not sure why this is thought to be a metadata issue - or is everything what somehow affects metadata supposed to go here no matter what the cause for the issue is?
I’ve just tested this - it doesn’t seem to be the case for the genres I’ve added to unidentified albums. Those get removed and re-identify doesn’t bring it back.
Interestingly, automatic identification of previously unidentified albums didn’t cause the “clean-up”. I will keep an eye on it when the next batch of albums gets identified tomorrow. If the custom genre sticks then most is fine. If I do a forced / manual identification, it’s not much trouble to reassign a genre.
Update: Indeed genre(s) assigned manually did stick while Roon did an automatic identification in the background again.
Summary: So it’s just when an identification is forced manually only genres from file tags are kept if set so in preferences but not genres (created and) assigned inside the Roon application.
Since I do know this now and nobody else seems to have a problem with it I mark it as (self) solved.