Location-dependent problems with PoE with confirmed-good components

Question

Project: 6x PoE IP security cameras. 2x PoE switches (3 cameras each) in two locations (house & barn) connected via a wireless bridge.

Problem: PoE switch, when installed in the barn, will only power 1 specific camera (always the same camera, a similar, but slightly different model to the others). Other cameras have powered on, and I have pinged them successfully, but they power down within a short while for no discernable reason. All cameras connected to the switch in the house work correctly.

After everything I tried today (below), my only theory is that it could be a power/interference issue. I could only test AC line voltage today (119V), and plan to try powering the barn switch with a UPS with active voltage regulation, but that feels like a long shot.

I won't be back in the area to test for at least a couple weeks... Would love to get some ideas or suggestions for things to investigate when I do.

Troubleshooting done:

1. Tested everything in the house. Everything works correctly.
2. Tested all cables multiple times. All cables work correctly.
3. Tested all switch ports with non-PoE device. All ports work regardless of install location.
4. Tested all switch ports with the sole camera that works in the barn. All ports work.
5. Swapped the switches. Whichever is in the barn exhibits the same problem.
6. Tested all cameras in both locations. All work in the house, only 1 works in the barn.
7. Tested the anomalous camera in the house with additional cameras connected. All connected cameras power on.
8. Tested barn switch with no other electrical devices connected/running to eliminate possible noise/interference. Same result.
9. Disconnected everything and tested again in the house. Everything works correctly.