Playlists not adding songs correctly - ongoing issues just got even worse

This has been going on for a few years now: When I add songs to a playlist, a message pops up that says “song X has successfully been added to playlist Y”. 5 out of 10 times however, the song hasn’t been added to the playlist at all, and if I just continue to add further songs, I’ll find that the majority of them aren’t there. (Meaning that it’s not just a synching or timing issue) So I now have to check the playlist after each song I add. If the song hasn’t been added and I add it again, it will then show up twice. Up until last week I was then simply able to delete the duplicate copy, however as of May 2021 I can no longer just delete the duplicate copy, instead, deleting one will delete both copies from the playlist. If I then add the song again, both copies will be added *again*.