I’ve been having various AirPlay issues for the last year, but one of the most annoying has been audio AirPlay streams stopping whenever my iPhone screen locked. I’d have to wake the screen and re-start the audio every time I unlocked and then locked my screen. It made using my phone while streaming audio a huge pain.
Turns out, this behavior was being caused by the iPhone’s very cool live lock screen feature. I imagine this is related to the fact that background audio will pause whenever you bring up another app capable of playing audio (which a live photo is). Setting a static lock screen made this behavior go away.