I regret to report that neither of those fixed the issue.
Switching to .pls format made it create a .pls file for the playlist that was most recently changed, but it didn't update upon subsequent changes. It also looked like it updated the most recent playlist when launching the program, but not any others.
Same story after updating to 3.5.8282.
Is there a debug logger that I could use to see what happens (or doesn't happen) when I love tracks that should be added to these lists?
EDIT: I just noticed that there was
a new topic for this issue opened a few days ago, after I'd found this topic via Google. In it, Steven says that "MB exports auto-playlists when MB is closed and anything in the library has changed." I did not know this, and expected the files to be updated immediately. I always thought they had done that previously, but I might be mistaken.
Anyway, simply closing MusicBee (after updating to 3.5.8282) seems to be the ticket here. It's a bit cumbersome, as I never close MB otherwise, but at least it
works.