Spotify has made it difficult to edit playlists when you are on your mobile application.
You used to be able to edit the playlist and the song you were playing was highlighted in green. You can no longer see the song you are playing so you have to remember the song and scroll through all your music to find the song.
Spotify should resolve this issue by (1) highlighting the song you are currently playing in green again or have that song appear at the top of the list, (2) allow you to search in the edit playlist screens, or (3) have an option in the menu (similar to add to playlist) that is "remove from current playlist."
This issue is extremely frustrating for people who have a couple hundred songs in a playlist and is an easy fix since they already had this functionality.