LattePanda Sigma Network Stopped Working

We have had a LattePanda Sigma running Ubuntu just about nonstop since we got it about 6 months ago and have had no problems. Then out of nowhere earlier this week, the NICs stopped working. Automatic updates are disabled, we didn't change the cables (it's all installed in a cabinet that is screwed closed), nothing else changed. We tried swapping cables and a fresh install of Ubuntu 22.04 with no luck. USB network adapters work, so there is nothing wrong with the networking on the system, just the onboard NIC. Ubuntu shows the 2 nics in `lspci`, but not in `ip link list`. Where else should we look for potential problems?