I replaced the faulty network cable and brought the SDR system back up.
The old network cable was solid-core wires. I’m assuming that one or more broke due to movement; it was in an area where it could be blown around by wind a bit. The new cable is stranded wires, so hopefully that’ll prevent further issues.
I did have to power cycle the setup a couple of times just now. I’m wondering if there is a significant voltage drop (although I’m way below the length limit for Power-Over-Ethernet). I’ll have to check that at some point or just relocate the SDR setup closer to the shack.
In any case, you can use them again. Remember: I change the frequencies occasionally. If you want a specific range covered, feel free to email me (my call at arrl.net will get to me) and request a re-tune; this can be used for testing or just to listen to any interesting signals you want to monitor.