RPC server is unavailable Windows 2016 server

If it was working 3 days then the first step is to review the system and application event logs 3 days from when it happened and look for any deltas. Then also think about what applications, GPO policies, or configuration settings have been pushed 3 days to start narrowing down your root cause. Also, review your firewall logs for blocked ports and logs that monitor network services.  The answer is try looking at all the logs available to find the culprit.  The next thing after that is a network packet capture of the Veeam application trying to make the connection to its destination and maybe the network capture will tell you why the RPC service is failing (your network administrator should know how to do this.. aka use Wireshark).

I looked at the Security properties for two different servers and found one difference. one that did not have a problem has SERVERNAME$ included in it.     I found nothing in the event log or GPO policies.