I was haing the same thing happen - double check all coding on the entities, the trainwatcher, and the cp_master.
If that fails - copy paste a knowing working one into your map - example - Using BoojumSnarks game play library I took out all the items for the payload version I needed and placed it into a new box - tested it to make sure it worked (it did). Saved and called it - pl_test_map-working.
Then I did all my modifiactions/addons into it - using that as a template - calling each successive version path_test_1,2,3 etc until I got the end result that I neded. Then, once I knew it was working, I copied/pasted the nodes into my map and linked them into my existing track.
The mystery of the jumping cart was solved - er - ok fixed - never did find out why it was happening - lol