Some years ago I had been diagnosing similar server NIC issues, and after many hours digging, Intel was able to determine the fault was due to the four-port server NIC being counterfeit. Damn good looking counterfeit part! I couldn't tell the difference between a real Intel NIC and counterfeit in front of me. Only with Intel's document specifying the very minor outward differences between a real and known counterfeit could I tell them apart.
Intel NIC debugging step #1 = verify it's a real Intel NIC!