I have two HomePods from original launch and three HomePod minis. All of them began to act strangely after the 15.0 developer beta of which I was invited to. Muffled noise during playback, disconnecting from wifi, no control via Home app, etc…. Most damaging is during the installation of 15.0 on one of the HomePod originals. It restarted to install and never recovered. Now is unresponsive and continuously blinks volume controls.
I called Apple Support and they offered no assistance multiple time because it’s out-of-warranty. Upon calling the 6th time and advising this issue happened via the AppleSeed beta 15.0 that they invited me to, the Senior Advisor arranged for me to have it replaced at no cost. My suggestion is keep calling until you get the right senior advisor that isn’t guarding Apple’s purse like it’s their own!