I have the same problem:
If it happens again I’ll check to see if the red light on the drive is on.
I also find it interesting that someone had commented they had some kind of credentials failure in the logs. I have one computer that always looses access to the My Cloud after a Windows 10 update. It will have access immediately after the update but will loose access after waking from sleep. I have to manually enter my network credentials to regain access even though the credentials are in the Windows credentials manager. I wonder if this has anything to do with it.