Hyper-V Generation 2 Centos7 VM With Differencing Disks

I have a centos7 VM running in a generation 2 hyper-v vm, working nicely with a base install.

I have created a new identical VM, with a new disk based on a differencing disk from my base VM, but it won't boot as it can't find the boot loader.

The master boots fine.

I'm running on Windows 10 for the host, and have a set of layered differencing disk based windows 2012 server instances working fine.

How come it's not working with Centos?