There seems to be a possible conflict between the above scenario and (maybe) the switcher DLC, as when you begin the scenario, your string of hoppers spawns with another loaded string inside them, overlapping. As soon as you couple to the empties, the scenario fails due to "train derailment"
This situation has been noted elsewhere in these forums and, I think, been fixed -- or at least is known to the development team.
I had another conflict with UP1 Northbound, where you're supposed to stop at Redwood Junction and leave a bunch of hoppers there... on an already occupied track... so I had to go around, reverse in and leave them partially on the switches blocking the GP38 supposed to unload them... I am very interested in my return trip...