Character mistake: Marion tells Robin "he chose you for a reason", despite not previously knowing that Robin was The Hood. So she has no reason to know that John chose Robin.
Robin Hood (2018)
1 character mistake - chronological order
Directed by: Otto Bathurst
Starring: Jamie Dornan, Taron Egerton, Ben Mendelsohn, Paul Anderson
Plot hole: Robin of Locksley is going round town with his black servant John with a metal hand (the only black person in the village it would appear too). John subsequently gets arrested later for being affiliated with Robin Hood. Despite him being not only the only black person the village but also the only one with a metal hand, the sheriff of Nottingham does not realise that Robin of Locksley is Robin Hood or even question why his servant is involved in the rebellion.
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Suggested correction: While it's anachronistic, he's very definitely not the only Black person in Nottingham.