I often find myself afraid to add songs by drag-and-dropping them into a playlist because of the uncertainty if they're added to the intended playlist and the lack of confirmation. When I drag-and-drop a song to the playlist menu this often trigger a scroll and on small screens I had trouble to hover over the right playlist. But this isn't the main issue, it is that there's no feedback to adding songs to a playlist. In some version of the iOS app there actually exist a confirmation that a song were added to a certain playlist. And that is great, because sometimes if you're not spot on with the cursor or do it way too fast the song maybe isn't added and sometimes I add songs to the wrong playlist this way not realising this. Nowadays I often check the adjacent playlist, but that is a result of this uncertainty.
I simply would like a better UX when drag-and-dropping songs into playlist. Visual feedback would help (e.g. the playlist that the song were added to gets highlighted afterwards or fades out from a distinct colour). A message would be helpful as well, telling me what song was added to which playlist.