Character mistake: Poirot talks with the Boyntons about the solution of the enigma after the dances, sitting at the table with them. By them, the British flag is hanging upside down from the wall - they are at the coronation ball, so not exactly a place where protocol does not matter. (01:29:05)
Character mistake: On the way to Jerusalem, Poirot says that "that man, Weizmann, put it rather well the other day, before Lord Peel's commission", and gives a famous quote about the world being divided in 'two places' for the Jews (those where they are not allowed to live, and those they cannot enter). The movie takes place in May 1937, and Chaim Weizmann's quote is from November of the previous year. 6 months are hardly "the other day."