I ran into another badly bugged mission across the border when I was riding with LP... this one was harder to get around.
About the time I got to thieves landing and forward a bunch of horses/horse carts were spazzing out and it was like there was a mini-earthquake right where that said there was sitting, lol. They couldn't move.
Also ran into a few problems where I'd shoot a buggy with bandits on it but it shot it when it was right infront of my and I wasn't driving the buggy (in shotgun) and the CPU driver was too dumb to back up or go around so we sat there for 5+ minutes while the buggy moved slowly, inch by inch, out of our way.
That's pretty much my only gripe - but I played a ton yesterday and probably wore out the game's engine (if that's even possible) because I didn't have any problems till very late. It was still a ton of fun despite a few of those bugs. I wanna beat single player before I try out the MP.