Archer's diving mask sits on his diving cowl instead of his skin. That would prevent it from sealing.
Cell phone reception is physically impossible under water.
When Jackov steps in front of Malory's binoculars, his face is clear. It should be out of focus and completely blurred, since he is right in front of her.
(at around 12 mins) One of Skorpio's bodyguards (all previously shown with black hair/mustaches) on the side of the chocolate fountain suddenly appears with shaggy blonde hair and a blonde mustache.