This is a known issue affecting vRealize Operations Manager 6.6 and earlier versions.
The issue is fixed in vRealize Operation Manager 6.6.1, To download,
Download VMware vRealize Operations Manager 6.6.1 In vRealize Operations Manager 6.6.1 the resiliency to networking issues has been improved and few flows suffering of the same problem have been covered and resolved.
Workaround:
If you are unable to upgrade to vRealize Operations Manager 6.6.1, perform the workaround by restarting vROps cluster as below.
From, vROps Admin UI > Take the vROPS cluster Offline and then bring Online.
Note: Ensure to verify and resolve if there are any network issues.