HomePod stops playing music randomly
I have 4 HomePods, 2 regular and 2 mini, in separate rooms, not set up as stereo pairs. When I use Siri on the HP or AirPlay from my iPhone, music will randomly stop playing. I've also noticed when using AirPlay from my iPhone, that the volume bar keeps jumping up and down, even though the volume stays the same.
Also, I have two different HomeKit scenes which start playing different Apple Music playlists. Each time music is activated by one of these scenes, the music will stop playing after 15 minutes. There's no option to have music stop playing after a certain amount of time.
I have an iPhone 12 Pro MAX running iOS14.4, and my regular HomePods are running 14.5 and the minis are on 14.4. My Home app says all HPs are up-to-date.
I've tried restarting my router and all HPs, and even factory resetting my HPs and re-creating the scenes.