Same issues here - it is a disaster. We see these alerts generating constantly, every single night, and nothing in the logs that would indicate what is causing the problem, no backups occurring, log entries are empty and all of the sudden VMs showing as disconnecting, then host not responding, then the disconnect, then sometime later, often times within seconds, but other times up to 40 minutes later, I see "Established a connection"..
I don't believe the VMs or the host are actually disconnecting from the network, otherwise, we would see other alerts triggered from our monitoring system that has hooks directly into the guest OS and would page our support staff.
I see the KB about increasing the handshakeTimeoutMs value, VMware Knowledge Base
And I agree that in many cases this could work to relieve the alerts, but then again, when these alerts appear in the logs they aren't being triggered and DO NOT even show up as triggered alerts in the web client under triggered alerts.. BOGUS!
We recently consolidated our vCenter installations from 4 to 2, so there are now more hosts managed under a single vCenter, but none the less, we only have 72 hosts. this is not a large inventory.. and we deploy vCenter as if we have max size environment...