Well, I've been having some trouble with this. I've been playing with a friend online and we started playing on veteran difficulty (he was the one that invited me to his game) but apparently I have been playing on normal difficulty while he has been in fact playing in veteran. Anyone know how I can change this? or how we can both play the same difficulty? Thanks.
This also happened to me. My friend who was hosting the game picked Professional difficulty but my game was registering it as normal difficulty after each mission. It has to be some kind of glitch. I managed to fix this simply by hosting the game myself and picking pro instead of my friend. So try switching hosts to fix it.