I had a 4th Gen Apple TV setup as my HomeKit hub and was working fine. Lately I've noticed the Home App on iPod/iPhone says "Apple TV not responding". I've done all the tier-one support obvious things: Updated iOS and tvOS, cycled power on and off, signed out/in on Apple TV cloud login, etc.
About at wits end, the Apple TV hub seems to be necessary for any newly added devices to show up on other home users (that I invited) iPhones. There will be unrest among the natives soon if I can't make this work.