So the issue was with the vCenter server (the Linux appliance version, which is a little disconcerning) not being in a 'ready state' to allow for migrations.
I restarted the vCenter server and everything started working as expected, immediately.
So the issue was with the vCenter server (the Linux appliance version, which is a little disconcerning) not being in a 'ready state' to allow for migrations.
I restarted the vCenter server and everything started working as expected, immediately.