At the end, when Faye Dunaway's character, Jane Wilkinson, is walking through the throng of press, the collar of her coat has a mind of it's own, changing position in every shot. It is off one shoulder then sticking up, then off both shoulders, then sticking up again and then off the shoulder once more. A glaringly obvious lack of continuity.
While on the talk show at the beginning of the film, Poirot says the last movie premiere he attended was Casablanca in Antwerp. Casablanca was released in 1942. Belgium had fallen to the Nazis in 1940 and wasn't liberated until 1945. It's highly doubtful Hitler would have thrown a movie premiere in Antwerp with invited non-German celebrities.
During Poirot's solution the long tracking shot of the dinner party during the flashback has been reversed as evidenced by one of the maid's walking backwards behind the seated characters.
During Poirot's speech to the gathered suspects (shortly before the 1:20:00 mark), he addresses Bryan Martin by the name "Mr. Marsh."