You just reminded me of the #1 reason.
Groot Multiball add a ball is busted beyond belief and can be worth +3 to -1 balls added into play if Groot is open. From the time you shoot the add a ball to the time the video for it stops playing, the game doesn’t account for balls locking into Groot as balls in play. It also subtracts any balls shooting out of Groot to the balls that should be in play, so you can LOSE balls with an add a ball:
So for example:
Ball added, net 2 balls locked in Groot between scoop and award = add 3 balls
Ball added, net 1 ball locked in Groot = add 2 balls
Ball added, net 1 ball removed from Groot locks = you get nothing
Ball added, net 2 balls removed from Groot locks = you lose a ball; the game will not return your next ball irregardless of ball save
Thanks for bringing that to mind @mwelsh! Until Stern fixes Groot, any competition at any level should honestly disable Groot to get around this silly bug.