I’m surprised other issues haven’t surfaced before now with 14.04. I can’t be sure this is related but it wouldn’t surprise me. It was a good release though, I ran it myself for years.
Debian 10 is a painless install on the Mini, and runs beautifully on it.
The only other time I’ve personally experienced your specific problem was after a power blip. The power went off, on, off, on in the span of a second or two. Despite the mini being plugged into a UPS, the mini restarted. HA came back seemingly fine, but I had no cloud connection and it wasn’t an option on the Configuration page. Everything else seemed normal. I powered off the mini, booted from a usb stick and did a fsck on the drive. Rebooted when it was finished and magically the cloud was back. It’s hard to imagine how that could cause such a specific error, or that the resolution would be a clean power down and file system check, but that was the only thing I did and it worked afterwards…