Hello, 

We have been having this issue for some time now and getting frustrated. We have a Server 2012 R2 Host running on a HP ML350 G8. It is running a Server 2012 R2 Guest using Hyper-V. The guest OS is attached to its own NIC on the HP Server (which comes with 4 NICS built it)

Every week, the guest server seems to lose connectivity to everything. The guest server is still on but all devices on the network can no longer access the shares or even ping the server. 

To fix this, the ethernet cable of the NIC connected to the guest is disconnected from the switch and then reconnected. The host server is running fine throughout. 

Why does this keep happening? It seems to happen like clockwork every week Thursday afternoon!