Homekit not responding on iPhone 13/iOS 15.4.1

I think there is a bug in Homekit hubs. I have an iPhone 13 running iOS 15.4.1 that was showing "No Response" for all my Homekit devices. All my other Apple devices, including an iPad running 15.4.1, an older iPad Air running 12.5.5, and an iPhone XR running iOS 15.4 did not have this problem: all Homekit devices reported in the app.

I tried several things to isolate the problem. Eventually, I zeroed in on my two Homekit hubs, which run different houses. The Homekit hub for my house in Boston showed up as "Connected" and the hub in my RI house showed as "Standby" when I looked at Home Settings in the Home app on the iPhone 13. The problem was occurring in my RI house. When I blocked the hub in Boston, which is an AppleTV HD running tvOS 15.4.1, everything started to work correctly. (My RI hub is the iPad Air running 12.5.5.) If I unblocked the Boston hub traffic, the iPhone 13 started showing "No Response" again, until I blocked it. Again, none of the other devices' Homekit clients had the problem.

This appears to be a bug peculiar to the iPhone 13. Next time I am in Boston, I will try rebooting the AppleTV hub there and see if the problem persists.

It took me awhile to find this. The documentation on how hubs work and the "Home Settings" command in the Home app are not particularly easy to find. There's got to be a better way here.