When Denzel Washington goes to his home, a policeman stops him, but later agrees to let him into the town. He tells a second policeman to let him pass through. When Dave's team arrives later, Dave shot the policeman who tells him that he cannot pass through, and the other policeman is no longer around.
After taking Amy to the hospital to get her stomach pumped, Robert pays a visit to the men that put her there. After he asks for their cell phones and any other video recording equipment, we see one of the men go to the door and lock it. When Robery leaves about a minute after, he doesn't have to unlock the door; he just pulls down the handle to open it. Rotary locks such as this work independently from the door handle.
The Belgian hotel's hallways have North American-style exit signs, beige quadrilaterals with "EXIT" illuminated in red letters. European-style exit signs are usually white-and-green rectangles, showing a stick figure running towards an open door.
The street-level establishing shot of what is claimed to be Brussels is clearly Prague, Czech Republic. There is a Czech strorefront sign on the right side and the Polish consulate in the Czech Republic on the left.
The Interpol is depicted as a murder-scene investigative agency, even allowing the CIA to cooperate and visit the crime scene. First of all, the Interpol is an international authority that facilitates cooperation among countries, with no law enforcement duties and powers on national soil (Belgium). Secondly, any involvement of a U.S. inteligence agency would be coordinated at the government level. The CIA would certainly not be allowed to walk around fresh crime scene.
When showing McCall, as a Lyft driver, insisting upon a five star driver rating from a passenger, after avenging that passengers abuse of a young woman, it showed him receiving the rating from that passenger. In fact, Lyft drivers don't actually see the individual rating from specific passengers, rather a rolling average of the previous hundred passengers.
CCTV systems in public hotels and other commercial service providers in the EU are not capable of recording audio, and often are not allowed to. A hotel would have no reason to have one, as it would require complex data protection disclosures incompatible with the services of an accommodation business.
When Dave is in the kitchen with his wife and kids, McCall enters and the wife tells Dave "it's one of your old Army buddies". But when the kid is hiding in the secret closet you see a Marine Corps. full dress blues uniform and at the end of the movie the kid sees a picture of McCall and his wife and again McCall is in a dress blues uniform. If McCall was a Marine then Dave was too and no Marine wife would make the mistake of calling them an Army buddy.......
During the final battle, McCall shot at the transformer on the pole, which exploded and generates a smoke screen, before he enters the bakery. He then cuts open bags of flour/sugar and turn on the fan to blow on the flour/sugar. There should not be any electricity because he just blew up the transformer.
When Robert beats up the men who abused the woman, he asks for any cell phones or cameras that they may have used. After the assault he never looks for them or takes them. This is made even more obvious because someone gave him a Lyft review after he left (which is it's own problem).
When Miles is hiding behind the two-way mirror and Kovac is looking directly at him (but can't see him due to the two-way mirror), the phone's light is illuminating his face. Kovac would have seen the light. In fact, Robert warns him of that later.
The goof item below may give away important plot points.
During the final fight scene, Robert sets a trap for one of the last remaining bad guys. Robert takes cover inside his wives old bakery shop, and cuts open multiple bags of flour and turns on fans causing a flour wind storm. Once Ari, the last baddie, attempts to breach the building by throwing a flash bang into the establishment, a large explosion is set off and Ari is thrown back across the yard. After a few camera angle changes, you see Ari in the air hit the ground, and bounce along the ground. You can tell this is a stunt man because suddenly Ari's face is a bouncing rubber mask.