Audio problem: There's a bit of a mix-up in the codenames of the cars who chase Reggie Dyer. Unit 7 is the first to give chase and it is identified by its crew with the photographer. Then Unit 8 intercepts at the rendez-vous point. Check the license plate; FVW 49. Japp mentions a "unit 10" that is not shown. Later in Chinatown, Japp calls for the other cars, and "Car 8" responds, but its license plate is now YD 8501 and it's another car model. Unit 10 is again not shown. They dubbed in the wrong voiceover, they should have kept offscreen the second response by Unit 8 and made it Unit 10's.
Audio problem: Nick gets supposedly grazed by a bullet fired while the plane's noise has already diminished considerably, making quite unlikely that any gunshot could be drowned out by it. (00:06:50)
Audio problem: When Hastings is caught off guard by the premature launch of the clay pigeon, he fires a couple of shots in a haste. Fairly obvious that he does not, and the mere sound of it has been added in postproduction. (00:01:40)
Audio problem: In an empty golf course, at such a close distance as shown, there's no way Miss Plenderlieth would not hear Hastings calling Poirot, who "lost another ball." (00:41:20)
Audio problem: In the very first turn of Monopoly shown, the player scores 11, but moves just 7 ticks. In the second, a 9 produces 8 ticks. (00:01:40)
Suggested correction: It is entirely plausible that a player does not tap the piece to the board with every move. Sometimes, you tap it hard enough to make a sound; sometimes, you just hover the piece over the square.