Continuity mistake: Agatha's nightgown strap switches between hanging down on her arm, or being up on her shoulder, normally.
Continuity mistake: When Zero and Mr. Gustav are discussing things in the courtyard right after Mr. Gustav escapes from through the sewer system, Zero's bag strap switches between across his chest and hanging by his side in different shots.
Factual error: The concierge in 1968 rushes to help a guest who is choking. The scene depicts him performing the Heimlich Maneuver. It was not introduced until the 1980's.