Do you have the schematic for the game?

I have zero experience with bowlers.

But on a Gottlieb EM pinball score reels get their power for resetting through a different circuit than when they move/score during game play. Something tells me you need to find the game play circuit that drives the reset of these and check those switches for timing/contact, etc.

It is possible the plungers/stops wear, but that should make the stroke longer in time.

Is there adjustment to the coil positions such that you can move the coil further away effectively forcing the plunger to a longer stroke that might get the straggler relays to latch?

Be careful to not adjust it too far. You don't want to overload the reset mechanism.