Hey, so I realize the focus is pvp at the moment, however, I've tried to run Underground to get gear and the achievements down there. In three tries at a 2 phase, challenging with a four man group we finished one because people were either getting stuck in doors themselves, or enemies were stuck in their own spawn doors and we weren't able to complete the operation. The underground would be awesome if it wasn't so buggy. It's almost not worth trying to rank your guy up in there because it's more of a hassle just trying to dredge through the bugs than it is actually leveling up. There are obviously many things that need to fixed but I really hope this is one issue that deserves a touch up at least. I mean we did pay for it.
I can be a little more exact on the bug description...
Take the missions type where you have to start up the generator and protect it. You enter the room and kill the initial NPC. Once you start the generator, more NPC show up. On some map types, these NPC are in a room in which the door will open, the NPC come out, and the door then closes. If the NPC stays in the room due to suppressing fire or grenades, it will then be trapped inside the room with no way to kill it.