The Adventure of the Western Star - S2-E9
Character mistake: While handing Mademoiselle Marvelle's letters to Hastings, Poirot calls him "Chief Inspector". (00:06:55)
Factual error: The Jarrow crusade was 5-31 Oct 1936. The sign posted at the hostel stated Poirot was speaking 5 April. (00:15:30)
Continuity mistake: Poirot gnaws the pearls Cornelia returned and deems them to be fake. He indignantly tosses them on the desk, where they show up in the following shot neatly arranged. (01:05:15)
Factual error: The night of the murder, before Jackie has her nervous outburst Ferguson is reading a magazine. It's Life magazine from January 1937 with FDR on the cover. The episode is set in January 1936 (as you can see from the date on Pennington's ticket).
Factual error: When Jacqueline surprises the Doyles revealing her presence on the boat, she was initially covering her face with the December 1938 issue of Vogue. The story is set in January 1936.
Factual error: Poirot gets on the train to London. The engine has an SNCF plaque on it. The video then cuts to the 1936 cycle race. The BCNF was not formed until 1938.
Plot hole: Much like the 1978 movie adaptation, in this version there is an absurdly short time elapsing between Linnet leaving the bridge table and the incident and murder; it's barely two minutes when she'd have to go to her cabin, do everything a proper lady of the time would do to prepare to go to bed, and fall sound asleep. That's because the witness character (Cornelia Robson here) in the novel is supposed to be droning about her boring life for a long time, but there are no gaps in her speech to imply that a long time passed - at most there's the waiter bringing a drink at the very beginning who sorta comes out of the blue.