sometimes when ball drains and bonus is collected, the inserts will show that the bonus it counting down but the chime wont sound and the score won't actually be added to the players score reels. it will just count down the bonus and that's it, then on to the next ball.
no, its not tilting when this happens. Can still flip flippers etc when bonus counting down, just no chime and no points added to score reels.

just started doing this.

im on it guys, thx. will report back.

UPDATE: i did all of the above (including tightening every switch stack) and its been ok for about 25 games so far. So not sure of the exact culprit because i did it all then tested it.
thx and happy new year