iBFT table lost / not found after iSCSI boot

[qon]

Here is a quick update after some progress I made: I fixed the windows legacy boot problem and I am now able to boot windows via legacy boot over ipxe/iscsi on all clients.
So the problem is definitely that the iBFT table is either not created or overwritten when booting in UEFI on that particular client.

In the meantime I have also tried a different Intel NIC, and also a Mellanox Connect-X 3 NIC that has an ipxe in its UEFI boot ROM, all with the same result. It works in legacy boot, but with UEFI it fails due to missing iBFT table.

I am wondering whether there is a simple way to check at boot time whether the iBFT table is created correctly. Apparently with UEFI the iBFT spec works differently and the table should be created as ACPI table.