Best mystery TV mistakes of 2017
Continuity mistake: When Hanna makes the list with names involving her past events, they differ substantially between the close-up when they're written and the final wide angle once the paper is finished. Check Alexander: first an irregular oval with a straight side, then a perfect oval.
Continuity mistake: Earlyish in S1:E4 "Growing Suspicion" there is a still photo of Christa Carlyle wearing a cast on her broken right leg. Early in this episode there is a quick motion shot of her handing out a T-shirt to another student. The cast is now on her left leg.