Continuity mistake: When Nathan exits the manhole in Barcelona his fringe changes style depending on the shot.
Continuity mistake: When Nathan prepares the Negroni the mixing glass is either parallel to the napkin or to the left of it. This changes back and forth.
Continuity mistake: When Nathan arrives late to work he extends his right arm to take his jacket off and then lowers it. From the opposite angle his arm is extended, and he lowers it again.
Other mistake: There's actually no need for two people in order to get to the chamber with the huge urns. You could easily just pry open the grate by the fountain, rappel down and bust through the final door by some means (or have both of the keys).
Other mistake: After the wreck falls from the chopper it starts moving forward with broken sails - with the anchor set solid in the reef.
Plot hole: Nate did not have his postcards from his brother with him when he got out of the car on the plane and certainly not when he was jettisoned from the plane. If the answer to this they were in his pockets, the falling from the plane, fighting, and being in the sea would have meant they were mangled, lost or extremely wet and mainly destroyed. Yet he and Chloe have them along with the map that Sully exited the plane with (another mistake someone else mentioned), as if they had arrived yesterday.
Answer: Jo and her mercenaries were at the wrong island, It's when they saw Drake go past them in a speed boat, and not to the island they were on, that's when they realised they had been tricked.