Once (or maybe even twice) the honor guard of marching soldiers in fancy uniform are a little confused about which formation they should be in and which direction they should march. They seem to want to follow the European out the door, rather than marching a different direction to remain within the room.
Many of the historical costumes are clearly modern. For example, in one scene, Catherine the Great is wearing a gown that zips up the back.
During the opening section of the film, in which the unseen narrator walks/glides through the backstage area of the opera that is being performed, there is a moment in which you can distinctly see the shadow of the boom operator following the camera.
Many extras look to the camera and they quickly return to a default mark.