Check the correct WMI related network ports are open on the scanned Windows servers (as well as on any firewalls in front of the given servers): TCP 135, TCP 445, TCP 49152-65535 (RPC Dynamic TCP port range)
Ensure that DNS records are correct for the given server – including both A, and PTR (reverse DNS) records. Bad DNS records can cause WMI failure. For AD environments, check that only a single IP address is connected to the A / PTR records for the given server, depending on what is the primary DNS name of the given server in the AD Domain.
Ensure the WMI service is running correctly. Restart the WMI service to ensure the service is starting correctly.