“No fault code when using the tool”.
Interesting. As IDWT said, when the unit encounters that fault to send it to the bottom, there should be at the very least a number 8 in the Mode box of the tool.

What shows in that Mode box when you arrive? If no fault, it would show the letter D for automatic.
There is too much to list to describe just what might be causing your trouble.

But clipping door locks, DOL/DCL open or closed at the same time during a run. Slowdown switches verses selector inputs and the timing of those at terminal landings. Low power supply voltage can cause hick ups. There are input output cards as well as the dogtail board known as the multiplex transceiver on the car top. Good luck finding any of those.

The more information you can provide, the better we can respond to your problem.

IDWT; Do you recall the personality jumper position to cycle the car on test? This might help the guy catch his trouble. I can’t remember!