I'm thinking hard, not taking it lightly, and can picture it all. And it happens with treble up?
So, nobody wants to have to do all their work over again, when you've checked it and it looks good.
You've made sure that the jack is wired positive to end pin, and negative to sleeve, not running backwards.
I see little can go wrong at the switch, except for excess solder in the works, and that is common but usually visible.
I would go to the place where you grounded the jack, and either re-do it, the solder connection, or replace that pot, if it got overheated. And check the lugs on the existing pot to see that they did not get loosened or bent.
Finally, look for any OTHER ground wire that may have come undone, particularly the ground to stop tailpiece or bridge. The earth/ground illustration in this diagram is non-specific, but needs to be done, for real. Good luck and welcome!
And here is a slightly different view, but technically the same in principle, though differing slightly.