HomePod won play in separate rooms

I have 4 HomePods, 2 of them paired. Like everyone, I've had untold issues with and logged many calls to Apple Support. But I remain ever hopeful that eventually this will all get fixed and actually work at least as well as Sonos did for me for years. The latest fubar: I'm playing music to the stereo pair in living room and go to another room and start different music playlist (from Apple Music app). That turns off the living room. I restart living room. that turns off the other room. So, I'm playing wack-a-mole, until I give up and put the same music on both rooms. Not using Siri to do this because I find it so frustrating. Any thoughts on why this doesn't work?