Hyper-V 2012R2 and Proliant DL360G9 loosing connection

We have two DL360G9 servers with the integrated 4-Port 331i NIC.

On these we have installed MS Hyper-V 2012R2 edition.

The Port#1 is used to connect the Hypervisor and one VM to the internal network.

On Port#4 we have a VM connected to the DMZ segment.

At random (about 3-4 days, sometimes each day) the Hypervisor looses connectivity

to the internal network. At the same time also the VM connected to the internal network is offline.

The connections on Port#4 to the DMZ still work ok.

When we deactivate the Port#1 and reenable it, then the connectivity is OK again for

the Hypervisor and the VM.

Drivers are at Version 16.8.4,

all MS patches are applied.

Any hints?