I am working on UEFI systems. Comparing the same file found in different locations :
C:\>fc C:\Windows\System32\Boot\winload.efi C:\Windows\System32\winload.efi
Comparing files C:\WINDOWS\SYSTEM32\BOOT\winload.efi and \WINDOWS\SYSTEM32\WINLOAD.EFI
FC: no differences encountered
I also made that comparative long time ago and I can assure you even the SHA1 of the two files is the same, but I also found during my experiments on this topic Install Win10XPE_x64 Flat or Compact Mode on VHD , that not always work the same (if using the usual path to boot a full OS, the PC may boot from a PE or not, and don't ask me why, as I don't know the per sure the answer, my theory is it depends of internal code in the Bios), unfortunatelly I didn't mentioned this findings in detail in that topic, just made a strong recommendation to use the right path, as it will work fine always.
Just going by the book, extract from a Win10XPE_x64.iso both bcd files (yes usually on WinPE they never use capital letters for them, maybe as a way just to diferenciate from the standard BCD), now run BootIce and open them and you will see the paths I mentioned are exactly the same.
But yes, as I said at first seen the path should not be the cause of a MB failure.
Let's analyze the info you have, in order to find a possible cause:
What have in common the MBs that failed:
Same Bios Builder
Builded same year (then Bios are builded in accordance with certain UEFI version)
The UEFI specs allow, and even going further promote that the OEM include certain mini programs specifically designed to run during the very first stages of UEFI boot to realize certain tasks supposedly mainly to improve security/safety/speed of booting process, if one of those UEFI programs went too far and is over protecting the BCD(s) to not allow/block the boot of unauthorized/wrong code if detected, this may be the also cause of the failures, so IMHO the Bios code with or without some additional UEFI program is the biggest suspect in this crime investigation, if possible as an extra precaution it is better always disable Secure Boot before working on the boot process or installing a OS (as an extra safety precaution, just in case), Or better (as I always do) just leave it disabled forever, as it is only good to protect MS pocket, forcing all people/companies that make drivers and programs to pay them to get the certification. It doesn't help to prevent any malware, all malware just laugh about it.
But only you know all the full info, and only you can put all pieces togheter, please keep us informed, as this info seems very important for all us here, experimenting very frecuently booting every kind of things.
And let me tell you why I recommend you to always use UEFI_BOOT, it is very safe because it DOES NOT use any of those paths to boot a WinPE boot.wim, it just let the Bios + the internal code into the OS boot process to handle the path to the target file. Basically it saids use this boot.sdi, find following X.wim file and boot from it. Please see attached pictures.
NOTE: BootIce is an old program written before Win10, I have found it does not work fine to create 10 PE entries, (my theory is it laks the GUID code for them), but no problem with any OS, or OS into a VHD or older PE(s), anyway it is very useful to edit 10 PE entries once they exists.
Hope this info was of any help.