To be short : some Windows NT 4.0 CDs crash the emulated state of the VM.
I'm testing (for science) if we can multiboot Windows 11 to Windows NT 3.1. However, Windows NT 3.5 is also concerned to this problem. And not by booting off the CD, also by booting into the hard drive. And litte bonus, I don't know which SP is preinstalled on the CD. I also think that this problem applies to Windows NT 3.51 as this version is build onto Windows NT 3.5, however, I cannot say for sure.
And before you ask, yes, I've done the tweaks to do in the BIOS. (Multiprocessor specifiaction to 1.1 as 1.4 crashes the Windows NT 3.x OS)