Hubitat webcore does not run in the cloud, it runs on the hub.
I just restarted the Hub in Safe Mode and the Web UI is at least responsive, so that is something. But none of my devices are responding to actions taken in the Web UI, both zigbee and z-wave devices.
webCore runs local on HE (editing a piston can either be local or cloud). Willing to bet that you could write the same logic into RM and end up with the same result.
I don't think WebCoRE is officially supported so am not sure what they can do..
Thanks for the clarification.
Safe Mode. This disables User and Built-In apps and devices, the scheduler is halted, the listener for LAN messages is stopped, connection to the Hubitat cloud is disabled, the UPnP listener is halted, and all Zigbee and Z-Wave devices are disabled.
Ah ok thanks. I will try disabling WebCore and rebooting into normal mode.
Next time you reboot, you may want to remove power to hub for about 30-45 seconds to clear the z-wave stack....
So shut down via 8081, unplug hub for 30-45 sec then plug it back in?
Yes
P.S. unplug from the power supply end, and not the Hubitat end.
That actually matters!?!?!?!
less chance of damaging the connector on the hub
Ha ok thanks. It looks like my WebCore app code is out of date so going to try updating that now.
OK I think I am good. It turns out that all three WebCore apps were updated on 12/8, which I think roughly aligns with when my issues started. While in safe mode I updated all three of these apps, then did the shut down/unplug/wait 30-45/plugged back in and now everything seems fine. Hopefully it stays this way. Will report back if any further issues. Thanks all for your help.
P.S. I inadvertently unplugged from the hub end but didn't break anthing! 
I'm happy to report that everything is still working fine this morning, so it seems the issue was likely WebCore being out-of-date. Thanks again for everyone's help.
Does anyone know how I can keep Webcore up-to-date automatically, or at least be notified when there is an update?
You should update your thread title adding [SOLVED] so folks know that "Serious Issues" have been resolved 
Done, thanks.
If you haven't already, install Package Manager, and then run a Match. This should register webCore with the Package Manager; Package Manager runs an update check every 24 hours and will notify you if you have an app or driver that needs updating.
Thanks will check that out.
You should probably also make it clear that it wasn't actually a serious issue 
Download the Hubitat app
