Samir crosses into the United States from or at Boundary Bay. This would be very close to the worst place to cross from Canada into the United States. The border crossing is the only access to a peninsula which contains the hamlet of Point Roberts with a population of several thousand. To access the rest of the States, Samir would have to rent a boat and go be sea to Bellingham or Blaine, or he could go back into Canada by road.
When Samir parks the SUV at the apartment complex on the street next to the basketball game, the driver's side front window is all the way down. When the police following him reach it, the window is completely up.
When Samir is talking to Chandra in the park, in Chicago, he is sitting in the center section of the three-section bench. When the FBI agents look at them through a spotting scope, he is instantly shown sitting within the left section, closer to her. In the next shot of them, he is back in the center.
In the prison yard when Samir is supposedly praying he ignores the guy threatening him and then when Omar comes in he's still in the prayer position but when the other guys leave he just walks away with Omar not completing his prayer.
When preparing bombs to use in the attack on the American consulate in Nice, Samir is shown with 3 presumably completed bombs. When he opens up his tool box to place the bombs, there are but two; this fact is later confirmed by Clayton and Archer at the scene.
When Roy and Max are on one of the freighters in Halifax, NS, the camera pans out to the harbour to show another boat and a distant bridge. The harbour is clearly not Halifax. Halifax has two bridges, which are suspension bridges, the bridge in the distance may be a cantilever or compression arch bridge.
A panning shot of Washington DC later crosses the Potomac, showing the Rossyln part of Northern Virginia. A building obviously in Virginia ends the scene, with text that mentions the building as a special operations office of the FBI in "Washington, DC."
In a briefing the fact is mentioned some of the terrorists were contacted by payphone in (among others) Amsterdam, the Netherlands. In the Netherlands hardly any payphones are left and as opposed to payphones in the US or the UK, Dutch payphones cannot be called directly, since their number is not displayed or issued anywhere.
In the FBI Special Task Force headquarters, the time on LED clocks in the background is incorrect. The GMT clock displays 14:17 whereas the Pakistan clock displays 01:17. Pakistan time zone is GMT+5, therefore it should have been 19:17 in Pakistan when it's 14:17 in London.
Samir states that they can avoid having their e-mails traced by logging on to each suicide bomber's account, editing the e-mails with mission instructions and then saving them as drafts, this way there would be nothing transmitted on the network. Then the bombers would login to their accounts and read the draft e-mail. Others have suggested the activity over the network to access the web mail account could be tracked. However, connections to web mail accounts are encrypted (https). In addition, tracking what someone is doing from an Internet café on the web would result in a lot of noise with very little value. More high-value information comes from tracking email, which has a sender, a recipient, and is unencrypted (and therefore would trace the network for law enforcement). Saving the mail in drafts is a very good way to significantly reduce the likelihood of the communications being intercepted in time to be of value.
During the scene where Samir is running into the apartment complex in Chicago while running away from the FBI agents, the original agents following him radio in that they are at the address "128 S. Randolph." There is no S. Randolph St. in the city of Chicago as Randolph runs East/West. However movie-makers frequently use nonexistent addresses, equivalent to telephone nos that start with "555-" to avoid legal issues.
During the scenes in Yemen, soldiers and terrorists are not talking in Yemen accent, instead most of them are talking in (Moroccan) accent. In other scenes they switch from classic Arabic dialect to Moroccan accent again.
When the London police are approaching the apartment building they're using two motorcycles and a van. The van, if seen from the front, clearly shows the Mercedes-Benz star, making it a Mercedes-Benz Sprinter but when the "SWAT" officers exit the van, the rear door says Dodge on it. The Dodge Sprinter was, at no point, sold in the UK.
When Samir goes to the London home shortly after the bombing in Nice, a black taxi is seen passing in the street shortly before he enters the building. Next day he hails a taxi after getting off a bus. It is the same taxi. Whilst this is possible, it is highly improbable, given the number of black taxis in London.
The goof item below may give away important plot points.
Samir minimizes the loss of life in the bombing plot by placing all the terrorist bombers on the same bus. Given the short time from their receiving their instructions until the time of the bombing, they would all have had to live in the same metropolitan area. This conflicts with Nathir and Fareed's description of the buses blowing up all over the heartland, and with earlier scenes of Samir traveling extensively to distribute the bombs.