Yeah I’ve already thrown this into the feedback thread. This is at the start of the service, as soon as you open the doors to load passengers, you derail.
Yes it happens when you waiting to depart, however I spawned on foot & took over the service & managed to make it to Victoria.
I added my experience of the service here https://forums.dovetailgames.com/threads/london-brighton-timetable-feedback-request.46530/page-3, it's the last post on the page