This is embarrassing!
I'm so mired in another Big Sur bug (which I think popped up in 11.1) that I completely forgot to mention it...
If I use a keyboard control - Apple supplied or Butler added - to manipulate my currently playing song, the next time I try to play it or anything else the play is choppy, i.e. it stutters and starts and stops and starts... usually until I quit and relaunch Music, but sometimes it corrects itself on its own.
The only reliable way for me to start/pause/stop a song is from within Music.
Giant PIA!