Discovered this today while making an AI train do a drop off.
Do not place your siding marker on or too close to the bumper at the end of the track. Leave the end of the marker about 10 rr ties back from the bumper. When you use AI to make a drop off to a siding that ends, it places the consist at the far end of the marker. If it is too close the car will collide with the bumper and derail and you get a consist tilt error and the session ends.