Hi,
Have you checked the status of EAM (ESX Agent Manager)? EAM is an app running with vCenter that's used for install and management of host modules (ie, VXLAN VIBs). It needs to be able to talk to the hosts on port 80. You can check it's status in the vSphere Client from:
Home -> vCenter Solutions Manager -> EAM (on the right) -> Summary tab (Health should be green). Also check the Management tab and look for VSM.