Hello, do you have iCloud sync turned on?
This might be caused by a problem with sync somehow. It is difficult to know why this has happened. Normally adding a playlist while synching does not cause or should not cause problems.

As a precaution, (backup your devices), then turn off iCloud sync on your devices, delete the iCloud sync file in case there is a corruption, then gradually turn it on in your devices allowing time to sync and stabilise before turning it on in the next one.

Reference information:
https://technimo.helpshift.com/hc/en...hooting/?p=ios