Using a simple PowerShell script to check for low disk space on servers I encountered an RPC error (“The RPC server is unavailable”) on some – but not all – of the systems when calling Get-WmiObject.
It all points to firewall issues; and the solution was to enable the following inbound rules on the systems that were returning the error:
Windows Management Instrumentation (WMI-In)
Windows Management Instrumentation (DCOM-In)
This did the job on both a new Server 2016 install, along with an old Server 2008…