Last night, I had a short-haul link go out (SXT lite5 ac, powered by a PowerBox Pro) that's been running fine for about a year. I found that it came back if I forced POE on, but I don't understand why.
It is, in fact, on the last interface on the PowerBox, suggesting power budget triage, but I can't find any portion of the budget that's even close to limitation. Lowering (numerically) its POE priority did not bring it back up, it had to be forced on. Once running, turning the interface back to auto-on kills it again. When set to auto-on, the interface reports "waiting for load." When running, a cable test at both ends indicates no faults. (When waiting for load, it shows normal at 0m on the first two pairs, and shorted at 5m on the other two, which I could believe makes electrical sense).
The units on 2-4 are two 912s and an LHG ac. All of these are very reasonable numbers. Nothing here exceeds 1A per interface or 2A for the box total. The voltage number matches that shown in /system health.
My own intuition suggests the culprit is bad sensing circuitry in the PowerBox interface, but I suppose it might also be a bad resistance indicated at the SXT.
Any advice?