Just follow these steps:
Replace the following files (I used the default installation):

/root/fogproject/utils/FOGiPXE/buildipxe.sh
/root/ipxe/src/config/usb.h

then fire:

/root/fogproject/utils/FOGiPXE/buildipxe.sh

and finally copy the files to the target folder:

cp -r /root/fogproject/packages/ftp/* /tftpboot

I found the solution for this issue here: https://forums.fogproject.org/topic/17997/booting-uefi-only-devices-with-usb-network-adapters-problem-and-solution

Thank you so much, that was exactly the solution to my issue!

Hi there,
after several successful imaging tasks, I’m stuck with a notebook that has no onboard LAN Adapter. IPXE.EFI is loading successfully, but then the network adapter that has loaded IPXE.EFI will not get active:

iPXE 1.21.1+ (gcf534)… (Brand new recompiled today)
Waiting for link-up on net0…
DHCP failed.

Using the iPXE shell, I found out, that the network adapter is not detected (I used another notebook with an onboard NIC, but booted from USB. Same behavior, but I could see, that theonly adpater that was found after loading IPXE.EFI was the onboard adapter, not the USB.

Then I cloned the IPXE github repository directly and compiled the IPXE.EFI from scratch. This time the IPXE.EFI is connecting the network adapter, but I get into an endless loop:

Next server: (correct ip address)
Filename: ipxe.efi
tftp://(ip-addess)/ipxe.efi… ok
iPXE.efi: 1041408 bytes [EFI]
iPXE initialising devices…
file:autoexec.ipxe… Not found
file:/autoexec.ipxe… Not found

…
And the back to:
iPXE 1.21.1+ (gcf534)…