Hi. I updated to Monterey 12.1 a week ago and now I'm having this same problem =( I don't have Home Sharing activated, and in my case the problem is happening very randomly and messing all the metadata in multiple scenarios.
Example, I rated dozens of songs a few days ago (after the update) and now, three days later, about half of those songs have the ratings disappeared. I start rating again and a few of them are losing the rating as soon as I open any other app and return to Music.
Playlists: I add a song to a playlist, and then a few hours - days later, the song is gone from the playlist.
And finally, I noticed is happening even to old songs that I just played. Example, a song that I added to my library like a year ago, was rated, and present in multiple playlists. I played that song for the first time in months, and a few minutes after playing it the rating was lost, it was removed from all playlists, it's like I just added it today (though the reproduction count shows correct number of plays).
This is extremely frustrating =(