I migrated to HomeKit (from an Alexa configuration) only a month or two ago and all this time I only had problems with unresponsive accessories. I have four HomePods, an Apple TV 4K, two MacBooks and two iPhones, with a combination of wired and wireless connectivity. As for smart devices, they are all LIFX bulbs and strips. Before 15.1, there was total nonsense about light bulbs that would work at one time and I could stay in the same location with three devices connected to the same account (my phone, my laptop and a HomePod mini) and all of them would report that different devices did not respond. I might control my lounge lights with my phone, but not the other devices; while those devices would control my bedroom lights, but my phone would report that the bedroom lights were not answering. After I upgraded my HomePods, ATVs and iPhones to 15.1, all those unanswered errors disappeared. Everything is connected, stable and synchronized on every device I own. I did a previous thread about all the issues I had and was told several times that my network environment was to blame. Maybe that was the case, but other than updating those devices to 15.1, nothing has changed in last week's network configuration or environment, and all of a sudden everything works flawlessly. Which certainly leads me to believe that the problem was software rather than infrastructure. However, he considers this a positive story: an update has fixed everything at once and, so far, has not broken anything else. I am very happy.