Deliberate mistake: The prisoners in the dark dungeon would not be able to read the letter (to Miss Dudley from Jason Flemyng that the carrier pigeon had) or see such a clear reflection by pouring water on the stone floor and holding the letter (written backwards) by the water. The room was suddenly lighter when doing so, but it wasn't clear where the light was coming from. Also, sunlight coming through the small window would not beam straight down along the wall. (00:07:23)
The Iron Mask (2019)
1 mistake
Directed by: Oleg Stepchenko
Starring: Jackie Chan, Jason Flemyng, Xingtong Yao
Trivia: Arnold Schwarzenegger's "performance" in this movie "merited" a nomination in the 2021 Razzies (Raspberry Awards) for WORST supporting actor, but he lost [or would that be "won"?] to Rudy Giuliani! Arnold's nomination had some good company: Chevy Chase, Shia LaBeouf, and Bruce Willis. Bruce was nominated for THREE of his movies - Breach, Hard Kill, and Survive the Night.