It's not only battery drain here, on my iPhone SE (1st generation) it makes making calls and doing various other things nearly impossible.
significant minority of iPhone users...
I’m on 13.5.1. Spotify has only used 1% of the battery in the past 24 hours. Not all audio apps that can run in the background have the problem.something is definitely worse since 13.5.1. My 3rd gen iPad air battery is getting murdered by Overcast background activity. Sounds like an OS audio bug.