why did kernel wimboot gui fix my issue ?

[bain19]

I had been using wimboot for quite some time, my chain loading pxe server looks a bit like this

Code:

lpxelinux.0 --> ipxe.krn --> wimboot -->boot.ipxe

everything had been going great, my windows MDT 2013 deployments were choochen along

My boot.ipxe was working with all our workstations models

boot.ipxe

Code:

#!ipxe
kernel http://192.168.0.1/release5_bin/wimboot
initrd http://192.168.0.1/release5_bin/bootmgr   bootmgr
initrd http://192.168.0.1/release5_bin/sources/boot.wim  boot.wim
initrd http://192.168.0.1/release5_bin/boot/BCD  BCD
initrd http://192.168.0.1/release5_bin/boot/boot.sdi     boot.sdi
imgstat
boot

then at some point we got new hardware and my boot.ipxe stopped working
HP 820 G3
Dell 5040


I did a couple things to try and resolve the issue but in the end adding "gui" to my kernel command resolved the issue.

boot.ipxe

Code:

#!ipxe
kernel http://192.168.0.1/release5_bin/wimboot gui
initrd http://192.168.0.1/release5_bin/bootmgr   bootmgr
initrd http://192.168.0.1/release5_bin/sources/boot.wim  boot.wim
initrd http://192.168.0.1/release5_bin/boot/BCD  BCD
initrd http://192.168.0.1/release5_bin/boot/boot.sdi     boot.sdi
imgstat
boot

Could someone tell me why gui command resolved the issue when everything was working without it before ?