Hey, you're awesome! That is indeed a workaround. I will update my Apple bug report to add this information as it should help them narrow it down. Seems like the Live Photos are causing the Airplay to stop. There is a similar issue if you are playing music on the phone and then open the camera app. It used to be if you were just taking photos, you could continue listening to music (such as via headphones), but with the new iPhone, any music will stop if you open the camera app, even if it's just on photos. In fact, even if you turn Live Photos off with the toggle in the camera app, you still can't play music with the camera app open.
Anyway, good find!