I'm rewatching PoA right now and it really ticks me off how they forshaddow Hermiones time travelling. Having her appear out of thin air during class just does not make sense. Sure she slipped up in the books here and there and disappeared but the movie makes it so obvious that it makes the student characters (I assume the teachers know about the situation) look lowkey stupid. I'm not the biggest fan of that movie adaptation in general but I can't think of another explanation for this other than "lazy writing"