This assembly is a pain to configure and adjust.

The DTs need to be able to drop when the mini solenoid for that target is enabled. It can be a random occurrence because the nylon tip on the plunger does not hit the target nib that drops it. There are two mounting scews that can orientate the individual mini coil brackets to direct the plunger inwards to impact the DT harder. It is not really an adjustment, but sometimes it works. They always "play up" with NEW DTs. Put the old ones back in and it will work most of the time.

Two balls into the shooter lane sounds like there are 4 balls in the game instead of 3. Sounds like the game is working in test mode, and playing up during play. Did you remove the apron ? Did you disturb the trough switches when lifting and dropping the playfield ? These switches can be a pain if they are out of adjustment.

Check the connectors to the CPU as well.