wimboot hangs at an Asus MB

[NiKiZe]

Are you using pxelinux->ipxe->wimboot, or just pxelinux->wimboot ?
but it works in all these cases if you only use ipxe without first using pxelinux?

You might get some more info from compling wimboot with debug enabled. But we do know from before that one some bios configs pxelinux->wimboot or even pxelinux->ipxe causes issues, often because of buggy bios or PXE firmware.

Since you have several machines showing this it should not be an memory error, but an proper long-running memtest shouldn't hurt.