Hi, I have also had all of my zigbee devices go offline at the same time.
I have 26 zigbee devices in my setup, a combination of smartthings multi-sensors, smartthings door sensors, smartthings leak detector, and GE zigbee dimmers. All of the zigbee devices in my network are showing as ‘unavailable’ and they are unresponsive in the app. 26 is a lot of non working things…
All of my zwave devices are online and functioning properly, as are things connected by WiFi and integrated through smartaps (ecobee, Arlo, Logitech hub). My Philips hue lights which are paired with a Philips hue bridge are also working fine.
The only thing which has changed/happened is that my internet was down for about 24hrs. If I go through my hub logs, the only odd thing I can see anywhere is a couple zb_radio_off events which I wasn’t manually triggering, but which I guess could be the hub trying to reconnect? (I am not sure, just trying to troubleshoot).