Factual error: Both the Yugoslav police officers Poirot is speaking to at the end are black. The chances of a black person serving in the Yugoslav police in the 1930s were zero.
Factual error: In the first frontal shot of Percival's Porsche following Lorraine, virtually every car parked at the side of the road is from after 1989, one of them not even being on sale until 2007. (00:16:10)
Factual error: In the credits, "they" would like to thank "the city of Landers, Wyoming." It is Lander, WY, as seen in the opening shot - not Landers.
Factual error: Sister Charlotte listens to Janice's confession. Only a priest is allowed by the church to hear confessions.
Factual error: The depiction of lasers is completely off in the movie. While surgical laser is indeed a real thing, such a highly concentrated beam with enormous cutting power seen in the film would take industrial size instruments and an extremely high power supply. Also, a laser beam simply doesn't look that way. Those scenes are way off into science fiction for an otherwise raw and realistic-looking thriller.
Factual error: One of the deaths involves a burning candle, a car and a leaking fuel tank, resulting in an explosion. This wouldn't happen. Multiple independent test evidence that petrol/gasoline can't be ignited this way, a flame isn't hot enough. Only the fumes can be ignited, which isn't what happens here, and the tank wouldn't explode anyway.
Factual error: The police Lieutenant Hightower is wearing the rank of Captain.
Factual error: The black leather chair of the Home trust banker is more modern than the movie setting in 1922. (00:59:35)
Factual error: The film informs us the gravity on Neptune's moon Triton is less than 8% of Earth's. But the whole physics of the rocks and his movement on the surface do not reflect that. The actual surface is frozen nitrogen. The difficulty he has in moving around is not well correlated by him only weighing 7kg. Https://www.imdb.com/title/tt5361488/.