does it matter which K?
spotting a K and hitting a bumper does the same thing ... tripping the 5B relay (bottom K) or 9B relay (top K). The main difference is the position of score motor when those relays trip.
take a look at the score motor 1C switch with BR-BLK and RED & WH wires ... make sure it's clean. well-adjusted and the contacts aren't horribly pitted.
if bank reset was only good when a center spot slick+chick target was hit (B relay powers) make sure the B relay make-break switch with BR-BLK on center blade connecting to OR-BLK or WH-GR wires isn't adjusted so all three blades touch at the same time. If they are, that could hide an issue with motor 1C switch.
the K bumper switches aren't sticking?
if the relay bank isn't screwed in correctly, sometimes a relay won't reset reliably. However, you'd have the issue regardless of how the reset was triggered.