@simon4 FWIW -- I have had a boatload of problems with Zigbee on my C8 (see thread here: Zigbee Storm) -- it took a long time to isolate the problem, but ultimately it was a bad GE/JASCO outlet that was taking my Zigbee network down.
NOTE: This is a device that worked just fine on my C4, C5, & C7s previously.
HOWEVER -- Devices go bad. As it turns out, I've had at least 3 of these GE/JASCO Zigbee outlets go bad. While this problem occurred somewhat coincidentally in time with my swap of the C7s to the C8s -- despite appearances I'm confident it has nothing to do with the hub itself.
I'd suggest that since you have a C7 handy, and a problematic device -- try swapping Zigbee devices to the C7 (one at a time) and see if the problem disappears or follows a device.
I do suspect that a "bad" Zigbee device can work "OK" on a lightly loaded hub, but it's problems may cause ore disruption on a dense network, and it's even possible that in a lightly populated network, a "bad" Zigbee device may cause NO overt problems. Hard to say though.
S.
