Audio problem: In the first ending, when it's revealed Miss Scarlet murdered four of the six people in Hill House, Colonel Mustard tells Miss Scarlet he has no more money when she wants to blackmail the guests. The other guests reply that they don't have any money either, but look closely at Professor Plum. Although Plum answers "Nor I" to Miss Scarlet, his lips are closed and don't move.
Continuity mistake: When Wadsworth is doing the re-enactment of the murderer killing Mr. Boddy with the candle stick, he pretends to hit Mr. Green. After he says "Will you stop that?!", Wadsworth grabs him with one hand. But when he throws Mr. Green into the toilet, he is holding him with two hands. (01:11:25)
Continuity mistake: When the 1st chandelier fell, we see Peacock and White are standing near the front door. Scarlet then says "look!" Bringing everyone to look at the dead motorist in the study. Peacock and White are suddenly teleported to the study door behind Scarlet, even though they were quite far away with even a couple steps to climb down.
Revealing mistake: Just before the chandelier falls, Col. Mustard quite visibly flinches, even though, realistically, he would have no way of knowing that it was about to crash behind him.