The lesson: always check for debris!

I recently did some revisions to previous builds, one of which was my "Tele-Strat".
I had it originally set up with a hardtail strat bridge and 3 strat pickups, but decided to rework it to a proper tele with tele bridge and pickups.

So, long story longer... it was all good after I made the conversion and played it regularly for a few weeks with no issue.
Then one day I picked it up and the bridge pickup had gone silent. After playing with the switch a bit, it appeared it was dodgy or maybe a short to ground (shielded cavities) because I could get the pickup to work intermittently moving back and forth from positions 1 & 2. No problem, I have another switch, easy peasy... done.

Worked great for a few more days, then nothing!
Then I discovered if I lifted the bridge pickup just slightly with my fingernail under the edge on the treble side, I would get sound. Now I'm thinking the pickup is shorting to ground and hopefully not a coil wire in the pickup.
I put it off for a couple more weeks simply because I loathed the thought of chopping off a basically brand new set of strings (yes, I'm a tight-arse).

Anyway, I finally found the motivation get it on the bench yesterday thinking the worst, a wonky pickup.
Turns out it was indeed a ground short, but not how I expected. There was a tiny off-cut of soldered wire (about 2mm long) floating around in the cavity that was intermittently shorting things out.
Because it was not just loose solder but also ferrous wire, it was magnetic and drawn to the pickup so I couldn't hear it rattling around in there when shaking or repositioning the guitar. It obviously did have enough movement that it would periodically break contact and allow the pickup to pass a signal though.

I have no idea where the point of contact was exactly, but once I pulled out the offending bit of wire and buttoned it all up, bingo! No more pickup cutting out!

I should mention that the pickups are Fender Gen 4 Noiseless and have a small PCB on the bottom, the short could have been between a trace, so may not have been such a big issue with traditional single coils. However, conductive debris floating around is never a good thing with any electronics!

So the moral of the story is always check for small loose bits of solder or wire or anything conductive before closing up your control or pickup cavities!