I play a guitar fitted with a Big Tone (bridge) pickup.

At almost all my gigs, it is fine. In fact many sound engineers comment on how loud it sounds (as did the luthier who fitted it).

However, at some gigs - about 1 in 10 - I plug in the 1/4inch jack lead and literally no signal comes out. Not a jot.

You can wiggle the lead around to no avail. Absolutely nothing whatsoever. Yet everybody else using that lead (eg at an open mic gig) has no problem at all. I plug the guitar into my amp, with my own lead, when I get home and it plays fine. Next gig, it's fine.

I took it to a luthier. He plugged it in. It worked.

I find this really inexplicable. If there was a wire loose, wouldn't the problem be more intermittent - wouldn't I be able to notice a difference by finding a "sweet spot" or somthing? I'm wondering if some 1/4 inch leads simply don't quite push in far enough somehow, or whether some leads are a fraction of a hair too slim or something... I can't understand it.