Those ust's (the wire rope types) drive me nuts. I don't have the fix, but can tell you I had the same basic problem with my Martin B1 bass.
After fussing for weeks, I finally ditched the ust and went with an internal (under the bridge) K&K pickup, ...best thing that ever happened to that bass. It was comprised of two transducers but I believe the 6-string model has three. No batteries, either. Nice units.
The problem is usually caused by low string angle over the saddle or an uneven saddle slot or saddle bottom. The saddle slot and bottom of the saddle need to be dead flat for full contact along the two surfaces. Re-set your bolt on neck angle and put a taller saddle back in it, making sure of a careful fit. There is also a case to be made here for adding string slots to your bridge, this would help immensely to even out downward string pressure across the saddle.
What may solve the problem is cutting the saddle it 2 pieces. Take a thin kerfed saw and cut the saddle into between the 3rd and 4th string. Reinsert saddle and see what happens. Cutting the saddle will provide even pressure on the transducer.
I made a slot, almost to the top of the saddle....No dice...Toast, I think...
Why I went to soundboard transducers, 15 or so years ago...