Comment 7 for bug 1918265

I'm also getting the same problem. Across 3x Windows 2016 machines running Hyper-V. Had this issue with Ubuntu 18.04 and now 20.04 but only when they are connected to a VLAN. My vlan assignments are 10,40,100,110,120,200 - I'm going to test next with an odd numbered vlan as that seems to be a pattern in all the above reports... I have tested and I get the same behavior if the VLAN is assigned in Hyper-V UI, from Powershell or even when using a default vlan on the network switch and leaving hyper-v unaware of the vlan.

Sometimes you can get the machine to boot by hitting Enter on the Grub boot screen (often 10+ attempts). A sure-fire way to get it to boot is to go into Hyper-V VM settings, untag the vlan from the network interface, hit Enter in the console to get it to boot and then re-add the vlan assignment. This gets very boring very quickly when repeating on multiple machines during maintenance and would love a fix or workaround.