The last few days my thermostat shows offline in SmartThings. It is still online in the Honeywell app. If I relink the service it shows as connected in SmartThings until I try to interact with it, at which point it freezes and than goes to offline. What is odd/scary is this message in SmartThings after relinking the device. It does not seem right to me, and not sure what may have been compromised. I have unlinked from Honeywell for now and reset my Honeywell password. Did the device itself get hacked? Or the device handler in SmartThings? Anyone have any ideas?
Good news —> your device has not been hacked. 
Bad news —> many users have been reporting certain devices are offline in the ST app.
Best advice —> report the issue to ST support.
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That nasty message seems to be occurring with a lot of cloud to cloud integrations lately. I’ve seen it in Arlo and Kasa, too.
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Are you using a WiFi or Z-Wave module (integration)? If it’s WiFi only ST support or Honeywell can fix it.
Thank you. As an IT engineer by trade, that message just seemed off to me.
There’s been a few outages on the Honeywell side the last few weeks. After a few hours and multiple attempts of linking the service, it did come back. It had been months since I had any problems, but here we are. I usually check down detector to see if the problem is honeywell or not. https://downdetector.com/status/honeywell/
Just looks like the internationalization of a message has gone tits up.