@zedx First I suggest you check if there is an update of the firmware for those devices available. Installing a firmware update can help.
You can also try different iPXE binaries for UEFI to see if it make any difference. Instead of the default ipxe.efi try snponly.efi and snp.efi.
If that doesn’t help you can try compiling iPXE from the very latest source code in hope of those fixing the issue. See my post here on how to do that: https://forums.fogproject.org/post/143521