No way, they actually found it pinched behind the panel? That's crazy. I can't believe you didn't find that until a late night call, those intermittent problems are the worst. Honestly my go-to is just a ton of zip ties and making sure nothing gets routed near a screw point. That's a brutal way to learn to check your cable runs.
Yikes, talk about a needle in a haystack. Of course it's always the one spot you don't think to look, like perfectly wedged behind that one bracket that never comes off. You finally find it and the cable's just sitting there, shaped into a perfect little oval from the pressure. The real kicker is when your own zip tie is the thing that did the pinching in the first place.