My home hubs keep going into standby mode. 3 Apple TV 4K, a HomePod and an iPad. All latest firmware. Short of signing out/into iCloud account on all devices again, anyone have any suggestions?
I'd try making only your HomePod a home hub to see if that works. I wonder if the devices might be each seeing that there are other home hubs so they can go into standby.
My other thought is that it's a network issue. Perhaps your network is killing connections when they're not actively being used.
I have two iPad Pros that I use as home hubs for HomeKit. One is always on standby. Check the home app in the settings to see which hub is connected and which ones are on standby. Only one hub can be active at a time.