Boulder, CO
I'd bet that when it kicks a ball into the shooter lane, the other balls in the trough are not rolling down into place...so they cannot be served into the shooter lane.
This can happen due to divots in the metal of the ball trough, switches that protrude too far into the trough, or even the balls being slightly magnetized.
In switch test, you're probably giving the balls enough momentum by dropping them in.
With the playfield in normal position, manually eject a ball into the shooter lane and see if the other two roll downward into place. I'd bet they don't.
