I was having problems “Saying Queue to Playlist, because I had too many playlists. So naturally I tried to DELETE the older ones. And there was the problem: I would delete them (Delete Playlist > Delete) and nothing would happen.
The solution: Make sure nothing is playing on SONOS while you’re doing this. Apparently using SONOS while trying to delete prevents it from deleting.
And when you DELETE a playlist, it takes a few seconds for it to disappear.
My system, Mac OS Catalina