If you are referring to the operations tab, it is a known bug. Due to the way the game handles baggage cars as "passenger cars", it can not be fixed at this time.
Due to the way the game simulates loads, right now there is no way to make the combine work for this use case. The combine is just a passenger car according to the code. The game currently does not support multiple freight types in a single car. Dev team will have to make the combines work in vanilla first before they can work for a mod.
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EDIT: My Railloader was incredibly outdated and it wasn't being recognized by the game(I never noticed somehow). Seems to work now!