Audio problem: There are American crows (Corvus brachyrhynchos) calling in the distance during the initial pursuit for Quan in the forest behind the Belfast farmhouse, right after the trap door scene ends and we see two of Hennessy's men share a look. American crows do not exist in Ireland - only hooded crows, carrion crows, rooks, ravens and choughs.
Audio problem: Just after K finds the 6 10 21 marking on Sapper Morton's tree, he begins to head back to his car. In the shot from behind K where he is first walking to the car, the only sounds heard in the shot are his footsteps and nothing else. The shot then cuts to an angle behind the car with the door opening, and it is now shown that K has set Sapper's house on fire, and the sound effects of the flames burning are suddenly heard. The sound of the flames burning the house should have still been heard in the shot where K was walking up to his car as the house was already on fire. (00:49:15)
Audio problem: When Richard is running around the house trying to find Jen near the end, he is heard ferociously breathing and grunting. The breaths and grunts appear to have been dubbed in as Richard's facial and chest movements remain mostly still, which wouldn't happen if he was breathing and grunting that heavily. (01:41:10)
Audio problem: When Hawk says "Damn, I'm out of bullets!", Michael Bisping's lips don't move. (01:17:20)
Audio problem: When John and another bodyguard/hitman are walking in a crowded subway/train station, and they're shooting at each other with suppressed 9mm or 45 ACP handguns across swaths of people and the people not reacting is an absurdity. High caliber handguns meaning anything larger than a .22 still makes a loud noise when suppressed. People in a general vicinity could still hear a noise and a pop. The only truly silent handgun is a .22 and it still makes a noise when the slide reciprocates back and forth. (01:18:00 - 01:18:45)
Audio problem: When Mercer confronts Mae about posting the image of the deer antler chandelier, there is a shot from behind Mercer where he says, "I can't be a part of this world that you're creating", but the movements of his mouth and jaw do not match up with what he is saying. (00:46:55)
Audio problem: At the Democratic National Convention when the female secret service agent announces that there is an active shooter, before firing her weapon, her audio briefly switches to sounding as if it were coming through as a PA announcement to the arena. Even though she's speaking into her walkie-talkie.