Very old thread, but i am running into the same issue.
Running 6.5.0u2
Or monitoring software needs to connect to 5988 (removed ip-adresses from following).
Test-NetConnection 192.168.x.x -Port 5988
WARNING: TCP connect to (192.168.x.x : 5988) failed
Firewall is allowed, CIMServer is running, also tried to disable firewall.