When Jackson is on the roof of the taxi, the driver fires his gun through the roof, making several holes. When the taxi crashes a few seconds later, there are no holes.
First two yacht guards fall overboard after being killed. When third yacht guard comes to investigate, he sees their bodies on deck before he is fatally attacked.
When Dellaplane kills his wife, he lays on the bloody body of her. Seconds later he stands up. The clothes of his wife is fully bloody but his shirt doesn't. It is absolutely clear.
In the opening scene, leading up to the assassination, the man killed fires 17 shots from a single pistol without ever reloading. The gun doesn't hold that many.
When Carl Weathers and Vanity jump out of the hotel window, if
you look carefully at "Vanity's" legs you can see that the stunt double didn't shave his legs for this scene, and his feet could never fit in her shoes.
When Jericho walks up to meet Patrice, and she storms out the door, he says: "Hi, I was just coming to see you!" After "Hi" his mouth barely moves. This is one of many scenes which have extensive ADR. Most of the outdoor scenes or dialogue in cars seem to be dubbed to various degrees. Also, the singing done by Sydney in the club is clearly play-backed. Though this could just be part of her routine.
When Carl Weathers and Vanity jump out of the hotel window to escape the police and onto the roof of his convertible parked in an alley, their impact reveals the mattresses inside the car covered with black cloth which comes undone at the rear window. You can also see the scaffolding at the bottom of the scene for the camera, also protected with a mattress.