I have three thermostats on Hub1, which is meshed to Hub2. My HomeKit integration is running on Hub2 with an Apple TV 4K as the primary HomeKit server.
I do have the thermostats shared with HomeKit, and after a Hub2 reboot, the “OFFLINE - device name” that is temporary with mesh is the name that promotes to HomeKit.
The device is online and updates on Apple Home, but the name doesn’t remove the “OFFLINE” until I bounce the HE application.
Not a big deal, just a bug.