I'm on easy mode; I killed all of the enemies, and it won't go to the next round. I was punching my shotgun bullets to kill the enemies.
Yeah I recently found that out too... Working on it right now, and for Maurice, I recommend killing the lesser enemies first, and then kill Maurice from a safe distance with charging your pistol (Hold m1 to charge, whenever you hear a sound, release m1 to shoot a charged/different shot, depending on what weapon, information tab is outdated :P)