I experienced a very strange situation whereby the Failover TCP/IP settings in a Hyper-V VM's network configuration stopped working after the Hyper-V host was rebooted.
Hyper-V VM settings:
A planned failover had been carried out that same day and the server was accessible as expected during that day. That same night I carried out firmware updates on the host Hyper-V server for this VM. After the host server was rebooted, the VM was not accessible. I discovered the Failover TCP/IP settings where not 'sticking'.
Actual IP address (DHCP) vs network config file
The Ubuntu 1404.3 VM has a static MAC address (as per best practice).
I rebooted the VM and it happily took on the static IP address again and all was well.