Thanks for the replies Guys and sorry for this late reply back.

I've ended up sorting this issue out, The whole problem ended up being with the set up in the VUK. It had no spring, no ball popper cup and the wrong armature assembly in it. The assembly was relying on the ball landing on the armature neatly when it dropped off the subway ramp.
A quick trip down to Mark C had me leaving with the right gear in hand, 20 mins worth of work (also installed a new coil and sleeve just for good measure) and she now hasn't missed a beat.

Cheers Mark.