Other mistake: Dante and The Agency both have extensive photos and videos of the team's previous exploits. Trouble is that most of it is simply stills and footage from the previous movies in the franchise, often occasions when nobody was around with a camera to witness and document what was going on, certainly not at the angles we see.
Other mistake: The Pit Viper John gets given has a 21 round magazine. When he's drifting around the bad guys at the Arc de Triomphe shooting at them, he fires more than that, without reloading.
Other mistake: Boyd calls an office in Rome, Inspector Lavazzi. Lavazzi is not in his office, so another officer, Valeria, answers the phone, saying a few lines in Italian (in the rest of the movie, she speaks English with Lavazzi). Shyann Yan is not a native speaker, which would be fine given her ethnicity, but she is also not a competent one. Surely, she is not competent enough to be an officer in Italy. (01:04:00)
Other mistake: The window looks closed, but even if the window is open, the woman ironing in her house across the parking lot would not be able to hear Jay and Maggie's argument from that distance, only muffled voices at best. (00:05:18 - 00:06:11)
Other mistake: Kristin takes a photo of her and Lorenzo and posts it to Instagram. A few moments later, her husband shows up and says he came to see what was going on because he saw her uploaded photo. She says it was only one photo. The photo was taken a few moments before. How did he get there so quickly all the way from the US? And came directly to where she was? Impossible.
Other mistake: Poirot receives a box of chocolates when he's home, then goes out shopping for eggs with the same box in hand, and in the next scene he's back home, having breakfast with the eggs. There's no apparent reason for this behaviour; who goes out for an errand bringing along a sealed box they just received?
Other mistake: In the cemetery scene, one of the tombstones is shaking due to the wind.