In Rail Journeys select "Great Western Express" and then for "Diesel Legends of Great Western" select chapter "Put a Gronk on it". When want to start last service "5X03 Coach Preparation" then after pressing "Get Started" button on the start screen locomotive immediately jumps into the sky and shows service failure due to derailing.
This should answer your post. https://forums.dovetailgames.com/threads/diesel-legends-5x03-derails-immediately.56215/#post-864626
