Continuity mistake: During the dance fight towards the end of the movie between Gru and Balthazar Brat the guitar/piano/laser thing swaps from a right-handed item to a left-handed one when Gru gets it.
Continuity mistake: When Bratt steals the diamond for the second time he breaks the window on the ceiling and glass starts to fall. Cut to Bratt and the falling glass disappears.
Continuity mistake: There had never been any signs of the ship being anywhere close to land, but suddenly the boat appears right next to a city when we see the minions flying past the ship. (00:05:15)
Answer: I'm going to assume you haven't watched the entire movie. There is a scene in the movie when all minions abandon Gru due to Gru not being willing to return to his prior lifestyle of being evil and committing crimes.
Rassdyt