I've not had chance to play much since launch but last night I did a Cajon Pass service and using the external camera I was moving around looking at the scenery and my wagons when I noticed that my consist was very short. It wasn't until I moved closer that more of the wagons loaded in (it really wasn't that far from the lead loco either, maybe 10 wagons). I also noticed that one wagon didn't load in at all so there was a gap in my train yet another wagon behind that which was loaded in, (getting much closer made it pop-in). I'll try and replicate it again and get a screenshot.
