Running on a 2-node cluster, Vmware ESXi 5.5 the symtoms are that a VM becomes unreachable, no ping replies, and wireshark shows no replies to any kind of connection to the VM. You can logon locally to the VM and then reboot it using the Console connection and then the VM becomes responsive again, but in a matter of a few hours, the VM loses network connectivity again. The local VM Operating System, Windows Server 2008R2 still shows the VM has network connectivity during the problem.
If you reboot the VM, the problem temporarily goes away.
The problem also travels between ESX Hosts after a VMotion migration. I have even shut the box down done a cold migration and restarted it. Within hours the problem returns.
If anyone has seen this before or has any ideas on how to resolve this permanently, I'd be really happy to hear from you.