When this happens to all devices at once it is most likely due to a PAN id change. The PAN id doesn't update in the HE UI until after reboot(!), so I suggest checking the PAN id at "http:///hub/zigbeeInfo" and then reboot and check again. If it has changed, you know why your devices dropped. How to troubleshoot and work around this is something I'm working on. HE is very quick to make a PAN id change, I have reported this and do hope they fix this behaviour, it is very much unnecessary to do the way they do, it only causes issues.
I feel for you, I've had this issue plague me for almost 2 weeks now. All due to ONE faulty packet sent by one of my Xiaomi devices about once every 24 hours. Very unnecessary to change PAN id and kill the mesh over something like that.
Download the Hubitat app
