Eu encontrei o mesmo problema.
Desativar o Hyper-v temporariamente resolveu meu problema e todas as opções de 64 bits estavam disponíveis:
I use hyper-v on my laptop. When I know I don't need VMs for the day, I can squeeze a bit more performance out of the machine by turning hyper-v off with:
bcdedit /set hypervisorlaunchtype off
and a reboot. To turn it back on:
bcdedit /set hypervisorlaunchtype on (or auto start)
and reboot.