Pre stretching cable/ Prop differences
personally I think what happens is that when you crimp the wire when new there is allways a tiny loop in the line around the crimp that under stress pulls thru until it tightens completely around the crimp tube, that and the plastic parts (horns etc) will wear just a bit
with time, also if you adjust the tightness on one end and the cable turns (not just the clevis) with vibration it will work it's way back out because you have induced a twist in the line