This is a known issue. In systems with two NICs, the 1st NIC in iPXE isn’t always the 1st NIC in FOS (fog operating system). This messes with tasking. Also, I’m not entirely sure if both NICs or just the first NIC gets registered.
A long while back, I suggested that we should loop through all the NICs in FOS and try to get an address on them one at a time, and with each one try to contact the FOG Server from each. Once a NIC is found to be successful, exit the loop and proceed.