Random drop of Hyper-V from network.

Hi

We have an HP Windows 2012R2 Hyper-V Server hosting 6 VM's.
The Server has 4 NIC's and 2 virtual switches. Each virtual switch hosts
3 of the VM's.

For a while now, and at random, one or other of the 2 virtual switches or
the NIC's they are bound to, loose there connetion to our Netgear physical switches.

We have tried swapping the NIC's Switches around, the cables, the physical
switches the virtual switches are connected too, to try and isolate a fault, but with no luck.

There is nothing in the event logs to show and issues of note and when the connection between the host and physical switches drops, the actual connection appears to still be intact. I.E. The host and physical switches both show valis conectivity lights, but the VM's or the physical NIC on the Server are no longer "pingable" and no data traffic occurs.

The fix is ither a reset of the Physical NIC on the Server (disable and re-enable in device manager) or a reboot of the physical switches.

We are unable to confirm if this is a Server or physical switch fault and as mentioned, this happens maybe once overnight every few days. 

Any ideas as to the cause?

Cheers