I had a similar issue in PS 5.1 after testing that it worked using the same credentials using PS core from a different device, though the error message was slightly different: "Restart-Computer : The computer SVRNAME is skipped. Fail to retrieve its LastBootUpTime via the WMI service with the following error message: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))."

The answer from @luke worked for me (specify the WSMAN protocol)