Good guess that you've got a failing board on your hands. Start removing NICs one by one. Reboot until you find the "odd man out," which will be the card that's in your hand.
goes apesh*t when hardware
The reason why I'm saying that this is "undoubtedly a hardware problem" is that the system was working fine, and
that it was beginning to report network-card errors, and the only
thing that you did was reboot. Obviously the device-initialization code is encountering those same errors. (Did you happen to notice which card(s) it was complaining about? If not, use the process of elimination.)