I had one mission from Dr.Z to kill a guy and collect something from his corpse but the item spawned below ground. Spent ages trying to find it. Turns put you had to leave area and come back etc.
Another one was on your typical 3 waves to defeat mission and after killing all of them in first wave, no new enemies came. I was locked in so couldn't get put to start again. Happened twice in a row!
Ignoring that I'm really enjoying the story and the dialogue, Handsome Jack is hilarious.