Starting a couple of hours ago all CloudKit request (both private and public database) fail with
CKError 0x114e01a10: "Service Unavailable" (6/2009); "Request failed with http status code 503.
CloudKit dashboard also fails to load private and public databases
The HTTP 503 "Service Unavailable" error, combined with the fact that the CloudKit Dashboard is also failing to load as you said, I would suggest to visit the Apple Developer System Status page (developer.apple.com/system-status/) to see if a CloudKit outage listed.
If the status is clear, please try again and let us know if the issue has been resolved.
Albert WWDR