I started getting alerts on Friday that my reports were failing to refresh. I looked into it today and, except for the error(s) on powerbi.com, everything looks correct: all automated tests succeed and the gateway app itself believes it is functioning properly.
I've updated to the latest version (14.16.6650.1) and restarted the service but nothing has changed.
You're right. I looked into the logs and it complained about a certificate being expired. I tried loading my PBI file and refreshing and got the same error. Turns out my SQL server's certificate (issued by my internal CA) didn't get renewed automatically. Not why that's happening but I don't think it's the problem of the gateway either.