The customer noticed that under the Application Windows system event logs, there were many error messages like this:
DCOM was unable to communicate with the computer ***.***.*** using any of the configured protocols; requested by PID *** (D:\***\Notification Server\Bin\AeXSVC.exe).
ITMS 8.5
It's due to port 135 being blocked.
Refer to KB 184952 "Ports and Protocols for Symantec IT Management Suite (ITMS) 8.5 and 8.6" to ensure the ports for AeXSVC are opened.