Plot hole: Spiro's vault can only be opened by Spiro himself, but the guards change every hour and Spiro doesn't go to the vault every hour of his life to let the guards in, so how do they get in?
Plot hole: The cube is suppose to be a tiny box, but Artemis retracts a keyboard from it at the end of the book. Surely that would be too small for your fingers to press the keys?