Shortly after the first seance, one of the two assistants is seen picking up two hurricane lamps (whch were still alight) by holding them at their tops. Something that would be impossible to do unless you had burn proof hands.
Desdemona Holland's real name was Dorina, however this name didn't exist in the 1940's in Hungary.
When Rowena mentioned obtaining the wildflower honey for "six lira". That is incorrect as the singular form is spelled as lira, and the plural form as lire.
The statue's hand upon which Ms. Reynolds is impaled should be covered with blood and gore, yet it is clean.
In her flashback scene, despite being a former nun, Olga Seminoff is seen crossing herself with her left instead of her right (correct) hand.
The two assistants were supposed to be from Hungary, however their first names are not Hungarian and their accent is not Hungarian either.
Kenneth Branagh decides to have Poirot lose his faith in God in the beginning of the movie, based on the evil he's seen in the world, only to regain it by the end. However, Poirot always steadfastly maintains his faith in God and truth throughout the entirety of the Agatha Christie novels.