In the treasure chest, teams received a physical Rubik's cube that was scrambled like this:
Each square has a letter, and part of a path. In the solved cube, the letters on each face have the same orientation, and the black lines form a continuous path that winds around the cube. (There are two satisfying solutions, but one of them does not lead to a sensible clue phrase.)
The solved cube looks like this:
Reading the letters along the black path gives the clue phrase SURNAME OF THE TEACHER WHO TAUGHT HARRY POTTER TRANSFIGURATION. The answer to the puzzle is MCGONAGALL.