System repair when toggling expose nested virtualization

I am running image backups of all my windows systems including Hyper-V installations. Most of the time, I can then later start virtual machines by just using the image as the OS disk. I can also enable nested virtualization and the run the existing vms in an extra sandbox or export them.

Now I installed a new Hyper-V system using a newer refresh DVD from evaluation center. Unfortunately for that version enabling nested virtualization causes Hyper-V to go into repair mode (no clue what I should repair then). Any idea why?

Both systems claim to be 10.0.17763 N&A Build 17763, but differ in the hotfixes listed. Drivers should be equivalent for OEM drivers, but for built-ins don´t know.

Any idea?

It is very convenient to know backups run virtually, and the fact that it does not work not just irritates but worries me.

Thanks, Joachim