Recent MS security update was the cause of this error.
An authentication error has occurred. The function requested is not supported Remote computer: <computer name> This could be due to CredSSP encryption oracle remediation. For more information, see https:/go.microsoft.com/fwlink/?linkid=866660
Reference article here
So temporarily you may uncheck “Allow connections only from computers running Remote Desktop with Network Level Authentication (recommended)” to resolve the issue Or make sure all clients & servers are updated with most recent patches.