If you are seeing bzImage being transferred you can remove iPXE out of the problem. The default you should have for uefi is ipxe.efi.
Now you should focus on the FOS Linux engine (bzImage). What version is the FOS Linux kernel? I know I have a Dell 7400 2 in 1 with a Dell usb c dongle (as well as a WD15/WD19 docks) that boot into FOS Linux and pick up a dhcp address.
I find it strange that it finds the network adapter, and sees the link come up but can’t communicate over that link. Lets start with what version of kernel are you using? The next part is to schedule a new capture/deploy task but tick the debug check box before you schedule the task. Then pxe boot the target computer that will but the target computer in debug mode so we can key in some additional commands.