So engine is cycling between fwd and neutral with each direction button press. Does the engine have directional headlights that indicate it "thinks" it's in reverse?
If you listen to the chassis can you hear a faint relay click when you first apply power (before sounds start)?
And you may need to turn volume down but can you hear the same faint relay click on every 2nd direction button press? It's rare but a defective relay can keep engine in fwd only.