L0 KVM and Win10 L1 nested virtualization not working (Windows boot loop)

A few months ago I set up two KVM hosts using CentOS 8.1.1911 with a Hyper-V VM as a nested guest and it all worked fine.

A couple of months later, I set up a third KVM host with a near identical hardware and software configuration. The only difference was the motherboard, which had the same chipset, but was Gigabyte branded not ASUS branded as per the first two. I set this host up on CentOS 8.2.2004 and experienced the same as you - bootloops. I tried the latest Fedora version at the time and it also bootlooped. As the nested virtualization on this host was not necessary, I just didn't use it and assumed the Gigabyte board was at fault.

Fast forward to today, when I decided to do an upgrade of my 8.1 hosts to 8.2. After the upgrade completed and I rebooted - the hyper-V nested VM's started bootlooping.

I rolled back to 8.1.1911 using yum history undo, and just like that, the hyper-v guest started working again.

TL;DR: might be a problem with the latest version of CentOS (8.2.2004). Try installing 8.1 (8.1.1911) and see how you go.