Nested virtualization, Windows 8.1 64bit, multiple CPUs lead to crash

[larisa_serova]

VirtualBox version 6.1.14
Host Machie: Windows 10 64bit (i9 9900K 8core)
Guest Machine1: Debian 10 64bit (4core allocated)
Guest Machine2: Windows 8.1 64bit

Host Machie contains Guest Machine1, and Guest Machine1 contains Guest Machine2, it's nested virtualization.

When I run Windows 8.1 64bit in Host Machie with multiple CPUs, no crash, everything is fine.
But when I run Windows 8.1 64bit in Guest Machine1, I can only allocate 1 cpu, if more then 1 cpu are allocated, it will crash after I click start.

Any ideas?
Logs in attachments.

[fth0]

The Guru meditates over a VERR_PAGE_TABLE_NOT_PRESENT error. There are already very few reports about it without nested virtualization, and even less with it. I'd suggest to file a bug in the Bugtracker.