FWIW, my C8 had a couple offline/online events after updating to 2.3.5.125. The Zigbee radio recovered and things are working, but had a few minutes when everything Zigbee was down. Took screen caps as I moved back and forth between the Hub logs and the Zigbee Details page to see what was happening:
At this point the channel displayed changed from 20 (normal) to 11
And came back to 20 after it was online again: