I have seen various issues regarding certain Broadcom drivers, and Hyper-V on HP/ Dell servers. A ping time between VMs on the same host can be 60-100ms and file copies painfully slow.
The advice is to disable the VMQ features.
Show all network adapters, look for the column “Enabled”
disable-netadaptervmq -name <adaptername>
Disable VMQ for specific network interface
Disable VMQ on all network interfaces
I found I was getting this in my test lab even though there was enough RAM spare on the host (approx 75% utilised only) turns out that Hyper-V is reserving a fair chunk of RAM automatically for the operating system (Server 2012 R2 in my case) therefore I just needed to lower the minimum reserve value.
Regedit – HKLM / Software / Microsoft / Windows NT / CurrentVersion / Virtualization
Create new DWORD “MemoryReserve” with value Decimal 512 to ensure minimum 512MB always remains after VMs are started.