Jazz bass pickups with treble bleed problem

That's how the treble bleed cap is supposed to affect the volume pots. Are the volume pots B250K ? That would be a linear taper volume pot.

EDIT: I looked at all the pics on the sale page and see the pots are audio taper. Audio taper pots have a narrower range than linear taper pots. For example from 0 to 7 you might not notice a difference in volume then from 7 to 10 the pot is all in. With a linear taper pot you see an increase in volume gradually from 0 through 10.

 

I guess you could check that the caps are 1nF ("102"), but TBH I'm not sure treble bleed caps would do much on a VVT. Notice the pickups wired to the centre lugs, unlike single vol guitars where the hot is wired to the clockwise lug. The treble loss with VVT is more to do with the resistance between the middle lug and earth, not the resistance between the middle lug and hot, where the bleed cap is.

I'm not sure I've seen a passive circuit, bleed caps or otherwise, with two volumes that didn't have this tonal effect. You are right, the volumes are essentially tone pots as well because they load the pickups more and more as they are turned down. That's exactly how a tone pot works (for most of its sweep, anyway).

You might have more luck with an unearthed blend pot instead of two volume pots.

 

Make sure that the legs of the treble bleed cap/resistor aren’t bent in a way that they’re grounding out to the pot or anything else.

They shouldn’t be touching anything except the lugs on the pot.