Hello,
Suddenly my heating is not working.
I see this…
Anybody else having the same problem ?
I already removed the integration and reïnstalled it, but it seems not to work…and now ?
Power off & on…and everything is back 
I’ve had the same problem. Just stopped working, now all of a sudden the integration won’t validate the PAT code. Nothing has changed my side.
When you say powered off on and back on. Which component?
I’ve powered the Smartthings hub, and rebooted HA and restored full backup.
I wonder if something has changed on the ST side.
I have two outdoor units (air to air heat pumps) for my air conditioning (cool & warm). A MIM-H04 hub is attached to each outdoor unit, which ultimately manages my indoor units.
With regard to switching off, I switch off the fuse (in the general fuse box) for 10s, so full power supply of those outdoor units and thus also those hubs is interrupted.
The interruption had nothing to do with home assistant. I was also no longer able to reach my devices via the specific app of Smartthings. This is actually the first thing you should check…
I hope this helps you.