Hi @MrBill, thanks for showing me that trick!
To be clear, don't believe that the issue is the RPi connection. At first, I thought it was my serial PLM, since that's directly plugged into the wall and is a common point of failure. But even with a new USB PLM and a new 2448A7 (this is getting expensive), the ISY shows no signs of 'network life'.
With most of these projects, I know enough to get by and to do basic troubleshooting. I was curious if the screenshot that I posted indicated a possible issue with the ISYs network port.
I experienced several very strange effects from this "surge", including having two ports on an 8-port switch (connected to a good surge protector) fail, having one zone on a lawn sprinkler controller stop working, and others.