Check the switch that registers it down. make sure the connections are good and the actuator isn't stuck. That switch takes a beating from the constant banging of the solenoids on that mech. If the game thinks it's down it won't drop it.

it's the microswitch on the bottom of the mech. The actuator has to be in the correct position too. between the metal tab and the drop target itself i believe

Tested with switch not your finger? Just checking. I've seen this switch work in testing but misaligned on the target mech itself. The actuator can find itself underneath the entire solenoid/plunger assembly where the weight of the plunger is activating the switch in game play. It has to be above the metal tab and below the plastic tab on the target that activates it. It can also get misaligned where it's not activating from the target when in the down position. If the game drops the target in test mode I would think it's a logic problem somewhere.