I had firmware updates to my mikrotik router twice in the past month or so and each time, after it rebooted, hubitat was no longer able to control my matter devices, although HomeKit was. So the Hubitat-to-HomeKit hub connection got broken somehow, and does not re-establish. Today I grabbed this screenshot showing matter enabled but status disabled. Clicking Disable, then Enable and the following reboot, got it back to working, im sure even just reboot would have got it working too.
I noticed this other thread with a similar issue, but a different solution. This feels like a Hubitat bug.
My Hubitat and AppleTV4K HomeKit hub are both wired to ports on the router. So each would have lost link state on the lan port when the router was rebooted. No IPv4 addresses would have been lost or changed, but I cannot be sure IPv6 link-local address wouldn't be different after the router has rebooted. Even if they are different, the matter connection should at least re-try, right?
Jon