Black Hole problem with captured balls

[PinballDude369]

Hello,

My Gottlieb Black Hole pinball has just started having a problem: when
you lock a ball into the lower playfield capture hole and then end up
finishing the game with that ball still down there the game doesn't
eject the ball first, wait until it comes back to the main playfield
to drain and then end the game completely. Instead, the game ends
while leaving that ball down there. When you start the next game it
then ejects that ball, the ball comes back to the main playfield and
drains. However, when you do start that next game a ball is released
like usual into play and once the lower playfield captured ball
finally gets back up to the main playfield and drains the machine then
releases that ball into play as well. You end up starting off a new
game with two balls instead of one. Can anyone tell me what's going
on with this? I'd appreciate it.

Thanks,

Rob