I have a mixture of HomePods (6) and HomePod Mini's (4). The HomePods are set up as stereo pairs, whereas the mini's are not. I have had continuous problems with them maintaining sound and all playing at once as expected. For a couple of months, it seemed that Apple had finally fixed all the bugs and my set up played quite well with only the occasional hiccup. Since I updated to iOS 15 everything will be playing fine, and then one of the HomePod speakers will make a loud pop noise and stop playing. Other times, I'll be walking through the house, and recognize that one of the stereo paired HomePods will not be playing while the other is. All too often, I'll be playing music, and it will just all go silent.
This is extremely frustrating, especially when I have guests over. Having to futz around with the stereo system just to get the speakers to work doesn't do well for Apple's brand, I can tell you that much. Having a dinner party where the background music just goes out, or Siri refuses to "Stop" all the speakers when told, or turns up the volume when asked to turn it down, or simply refuses to play on all the speakers when told to, loud popping noises that force me to restart the speakers... seriously? Why not just iron out the kinks before adding new features? Makes me regret investing so much money in them and return to wired speakers, that well, just worked.