Other mistake: At the very end, the Durmstrang ship is leaving, it's away from the 'bank', firing its cannon. And then we see the Beauxbatons girls leaving Hogwarts... Followed by Durmstrang students whose boat has already left. (02:22:00)
Visible crew/equipment: After Fred and George drink the aging potion and jump within the "age line", right before they say, "Ready?" and drop their names into the goblet, at the start of this shot the actor's T-mark is briefly visible on the floor, just before one of the twins promptly steps to that area. A bit of a second T-mark is briefly seen as well, to its right, also where the other twin soon stands. (00:30:10)
Audio problem: Just before the Death Eaters attack the tents, Arthur Weasley says to Fred and George that "Ginny is your responsibility", but his lips don't match what he is saying.
Continuity mistake: During the scene in which the Tri Wizard cup is brought into the Great Hall and then Harry's name comes out of the Goblet of Fire, pay attention to Hagrid. We first see him move behind Snape and Moody who are in front of the window and standing directly behind them. Then he is further over to the right of the screen in front of the wall, and then back to his original position.