Last night, my Hubitat Android Dashboard alerted me to an HE update. Having nothing better todo - I backedup and ran it.
A few minutes later, my HE was back up and running but I had a system message in the top right corner. Clicking it said 'Zigbee Network down'.
This was a first. I've done upgrades many many times and never have seen this before. When I went to the http://hubitat/hub/zigbeeInfo page - it showed Channel 11. I don't use 11 I use 15, and have for a very long time. I clicked on the drop down changing it to 15 and pushed changed channel. It came back with '11'. I repeated the attempts to change it. All Zigbee devices were down (Alexa would ding but nothing would change, no motion updates etc).
I went to settings page and pushed Reboot. After the obligatory few minutes - the hub came back online and things returned to normal. Zigbee details said Channel 15 again.
I didn't take any log snaps to offer here.