Currently functioning for me.
I was down for a couple hours with this too, but it seems to be back up know.
As of this morning I am still getting 504 Gateway Time-out. In the other thread some spoke about rebooting the router to get temporary relief. I am not sure why that would make a difference when this error is coming from external servers but will give that a try this morning.
HTTP 502 / 504 Meaning
To preface this, I'm not privvy to the inner workings of the Hubitat Cloud Relay, so this is just general feedback about what the HTTP 502 and 504 codes mean and why restarting the router could be a reasonable troubleshooting step if the Cloud Relay issues seem to be limited to your hub and others aren't having issues anymore.
HTTP 502 and 504 codes are typically used when a server is acting as a proxy for forwarding messages onto another server or endpoint. The 502 typically means the server you are talking with tried to talk to the upstream server / endpoint and it got a bad response whereas the 504 typically means it tried to talk to an upstream server / endpoint and it didn't get a response at all.
Again, I'm not privvy to the inner workings or implementation of Hubitat's Cloud Relay, but a 502/504 could certainly be a reasonable response if the Hubitat Cloud Relay had issues talking to your hub.
That being said, it could also be a reasonable response code for when the Hubitat Cloud Relay had trouble talking to other 'servers' that were needed for making the connection -- for example, a database for looking up details or even a message broker for delivering the message to your hub.
Unfortunately, the error response would need to be enriched with more detail to really know what it was complaining about.
Further Troubleshooting Steps
In the past, when I was able to reproduce these issues and it was a general issue with the Hubitat OAuth servers impacting everyone, I was also able to reproduce the issue with any Hubitat integration that used the Hubitat Cloud Relay such as IFTTT and Google Home.
If you have access to either of those, can you try reauthorizing them and see if you get errors as well? If so, you might try reaching out to the Hubitat support team as they might have better tools / logging to diagnose what's going on.
