The design contains a train module which changes its direction autonomous. The train may also trigger further actions at direction change time. The gear system must transmit huge power from the motor to the direction change part. And there the gear system has a weak point in the following figure below orange circled.
If this part is not build solid, the gear-wheels overrunning very fast. We need a couple of tries to build this part solid in a way that this not happen. I've created a Lego Digital Designer model for you. It shows out implementation of the Akiyuky design of the train. Rebuilding the design is very simple.
The whole model must not been built filigran. The train must have a big weight, so that the Lego train wheels do not spin. I propose to move the battery box toward more to the drive wheels in our model. That may only bring a little more grip and makes the model a little more reliable.
An additional weak point - were I found no proper solution yet - is the suspension of the driving wheels. The axes become loose over time and travels on straight line press on after about 30-50 again. With curvy rails more often.