Continuity mistake: In the first Now You See Me, Dylan said before his father got into the safe that was dropped into the river he gave Dylan his watch to hold so he could count the seconds until he escaped, but in Now You See Me 2 there's a flashback that showed what happened before his father got into the safe and he does not give him his watch. Instead it shows Dylan and his father both with a watch and synchronizing them together.
Revealing mistake: When Dylan is looking at the news articles in Thaddeus' cell, the camera pans over to one of the articles with the headline, "I am a victim": Thaddeus Bradley. The opening paragraphs on the first column are repeated throughout the entire article.
Continuity mistake: When Walter Mabry is explaining how the Horsemen ended up in Macau he walks over to sit on the couch to show the slideshow of the plane trip. As he walks over, Atlas is not on the same couch as the other Horsemen, but when Walter goes to sit down he squeezes between all of the Horsemen with Atlas now on the end of the same couch as everyone else.
Continuity mistake: At the launch party, Dylan is holding a playing card with 'The Fool' written on it. Dylan turns the card around whilst holding the card on the right hand side. From a different shot, he is holding the left hand side.
Other mistake: Merrit claims he has never ridden a motorcycle and talks about how unsafe it is, but is seen riding one in the first film.
Continuity mistake: Jack is shown wearing a security guard uniform throughout the entire infiltration of the launch party. When the party has been intercepted and Jack is exposed to everyone, he is still shown wearing the security guard uniform, but when the Horsemen are on the roof minutes later, Jack is suddenly back to wearing his leather jacket and T-shirt. Even if this is needed for the story and some time had passed between scenes for him to change, Jack was being chased by the FBI and was in a hurry to escape the building, so he would not have had anytime to change back, nor would he have risked wasting any time changing his clothes anyway.
Visible crew/equipment: The remote controlled camera is visible in the scene where the truck full of the horsemen is pulling into the garage. Look as the camera pans down and we see the top of the van. The camera looks like a box attached to some poles.
Continuity mistake: When Daniel is performing in London, there is a wide angle shown in the scene, with Daniel under blue lighting. In all other shots in the scene, he is under white stage light.
Answer: The only ones who knew the chip was fake were the Horsemen, no one else did. Walter did not know the chip was fake. The plan was to convince Walter that the chip was real so that they could lure him out of hiding with Walter attempting to kidnap and later kill them, and expose Walter to the public in doing so. They told the crowd after exposing Walter about the chip, because while it was a fake, they still had plans with it assuming it was real. If by "alert the FBI", you were referring to when Dylan gave the FBI director the evidence on Walter and Tressler, that was not the chip he gave to her, that was a hard drive containing all of Walter and Tressler's past dealings.
Casual Person