I can boot with UEFI: PXE, but not with UEFI:HTTP on my x4. On my X2L both UEFI:PXE and UEFI:HTTP works fine (IPv4)
HTTP UEFI boot on X4
Ok, I managed to get it to boot if I set the boot url manually (it should support getting it from the DHCP server) - and then it only supports https.