IP Cam Stopped working

Christmas eve one of my POE IP cams stopped functioning so remove an existing easily accessible cam as a replacement, out with the ladder & swap them over.
Back down the ladder & test. No good.
Swap the ethernet cable to another POE port. Still dead.
Find cable tester, back up the ladder. Cable tests good.
Diagnosis : camera ok, ports ok so must be the cable. Luckily have a spare 5m cable in the spares box.
Yesterday (before the rain & snow), replaced the cable which required accessing gable end from inside the attic & outside from the ladder.
Camera working again.

Laid out & inspected the old cable & found one section where the internal wires showed as twists on the outer.
Retested cable, all ok. Put some tension on the cable & got a fleeting reading of two wires showing at once.
The camera or cameras (there have been several), have worked fautlessly over the years. Presumably I had either stretched or created a knot in the cable during the initial install but the damage wasn’t sufficient to create a fault.