Ethernet connection to Mesa 7i76e disconnecting on its own after one minute

I had a problem with a Mesa board disconnecting a couple years ago.

Turned out it was a bad/weak DC-DC power supply.  Voltage would drop intermittently, causing the Mesa to reset and I'd get the 'error finishing read' nightmare.  Looked like a network issue, but @PCW helped me diagnose it as a power problem.

Maybe double-check whatever is powering the Mesa and see if it's dodgy.

Also make sure all power management is disabled on the host PC
Similar issues can come from Ethernet (EEE) or PCIE power management