Not an answer but a thought on how to divide and concour this issue. I have seen it before and we ended up with a new bios update on the one system model that was getting it but not likely the issue since you have 5 models of systems.
Do check the UEFI, and Legacy settings to see if one over the other is working. If one works and the other doesn't maybe there is an issue with the .efi files being created by the PXE server. Make sure you have added both 32bit and 64bit windows to the pxe server. Even if you only make a 64bit boot option having both some times will make a difference for some reason.
Are you using option 66, 67 on the domain controller? If so set up iphelpers on the switches instead as the forced mode 66 and 67 can cause issues in some environments and definatly does when mixing uefi and legacy systems.
On the PXE configureation utility, under the PXE server tab change the DHCP server discovery from Auto Detect to the proper solution I have seen where the auto detect can be a problem. Not specificly this problem.
How about teamed Nics on the server? I have seen teaming software modify the behavior of the nics and not always work correctly for things like PXE, multicast, some of the less common things. PXE is important but not common as far as use goes.
Cheers