Why my Apple TV stopped functioning as a Home hub

If you have been tearing your hair out trying every suggestion -- reboot everything, unplug router, etc etc -- to get your Home apps and devices working again when they suddenly quit, here's what just worked for me.

Everything was working just fine until I updated to TvOS 27 yesterday. Suddenly, all devices became unavailable and apps such as Eve and Home started showing them as unavailable and warning that I lack a hub. Huh? I tried all the suggestions found online and some of them worked for a few minutes, then back to "unavailable."

The problem turned out to be that the TvOS 27 update somehow logged the Apple TV out of iCloud. I logged back in under Settings, selected a "Room" and suddenly it began working again as the hub. Hope this helps someone.