hm2/hm2_7i76e.0: error finishing read! iter=25403

I would not just use one core but you can use isolcpus
so LinuxCNC uses only one processor (the last one
so if you have a 4 core machine isolcpus=3)

When you say USB card I would be suspicious if its not
a plug-in dongle (try testing with the cards disconnected)

I'll try that out. See if I can make linuxcnc crash pulling the usb based wifi card.