Spotify crashes when I attempt to delete a song from a playlist. It only happens when I am playing a (different) song from the playlist. If no music is playing, I can delete a song from the playlist with no problem.
Pertaining your issue, that seems like it shouldn't happen given what you’ve described (I've tried on my end and it works perfectly fine), I guess your music cache is corrupted, kindly do a clean reinstallation following the steps below:
Click into your Spotify App -> Logout from Spotify (Spotify app Settings -> Logout) -> [If you are on premium and have songs that are on available offline, click here: https://www.spotify.com/sg-en/account/offline-devices/ and remove all devices -> Go to iPhone Settings, General, Usage and Delete the app -> Go to App Store and download the Spotify app again.
Also clear off Safari’s Cache under iPhone/iPad Settings > Safari and Clear all of the caches.