I thought I might start a known fixes thread, as this may help people who have been spending hours attempting to get out of a bug.
Hall of Weaponry, Arindale - fix
When exiting the hall of weaponry when playing multiplayer with exactly 3 players (sometimes happens with 4 or more) a player will be stuck in the roof. When playing with 3 players you will need to save the game inside before exiting the hall and then load a fourth player into the game in order to exit propoerly HOWEVER some players may spawn in the breeding grounds upon exit. With more than 3 players I have found that 75% of the time there is no issue with a player being stuck in the roof, however they still spawn some in breeding grounds and some outside the hall of weapons.
Fargrove West Gate / South Gate lead into the Sewers - no fix known
I have tried several suggestions for this and in the end have just restarted from scratch. If anyone has a 100% successful way of getting around this please elt me know. The suggestion by DC of the south gate does not seem to work.