After Rebooting vCenter Server 6.5, you see these symptoms:
Note: This issue affects NSX Service Deployments (such as Guest Introspection and third party anti-virus or network VMs) running with vCenter Server 6.5.
VMware NSX Data Center for vSphere 6.x
This issue is resolved in vCenter Server 6.5 Update 1
To work around this issue if you do not want to upgrade, contact Broadcom Support