Update September 15:
Someone reported that after installing this update on a HP Gen7 the problem still exists.
Hyper-V virtual machines running on servers with Emulex network interface cards can randomly disconnect from the network when VMQ has been enabled. This is experienced by many. The issue both occurs on Emulex cards as well as on OEM Emulex cards. HP servers and some others use those Emulex 10 GbE cards.
See my earlier post for more info.
Today HP released a new driver which solves this issue. The driver is included in the Service Pack for Proliant 2014.09.
However Emulex advised odd ping may still drop but no disconnects. In the near future Emulex will do a complete rewrite of the driver to also fix the dropped pings.
Tim Johnson was so kind to keep me informed about this update. He told me after installing this driver update he did not experience disconnects for the last 7 days.