The door of the Mrs. Inglethorp's room (that had been broken in at her death) is fixed in the early morning before Poirot's arrival.
When Poirot starts to rebuild the house of cards, he first leans two vertical cards against each other then leans the five of spades horizontally against them. However after a brief cut to Captain Hastings the horizontal card has changed to the two of spades.
The story is set in 1917 and shown at the beginning of the film says, "General Haig attacks..." yet Haig was promoted to Field Marshall on 1st January 1917 so would not have been called General.
The opening scene is set in June 1917 and Hastings is wearing Service Dress uniform of the British Army. However, he is wearing Overseas Service Chevrons on his sleeve, which were not created and authorised until December of that year.