10. Giant Man Outta Nowhere - Avengers: Endgame
A movie as epic as Avengers: Endgame was always going to come under intense scrutiny when it hit home video platforms, and fans quickly noticed a baffling continuity error during the film's insane final action sequence.
At one point, Ant-Man (Paul Rudd) and the Wasp (Evangeline Lilly) head to their van in an attempt to get the quantum tunnel operational, yet mere seconds later when Black Panther (Chadwick Boseman) is shown running with the Infinity Gauntlet, Giant Man can be seen fighting a Chitauri Leviathan in the background.
Though it's clearly nothing more than an editing mistake, some have tried to hand-wave it by suggesting that either Ant-Man teleported into the battle and back again, or more hilariously, that it was actually Hank Pym (Michael Douglas) fighting as Giant Man.
Either way, fans kicked up enough of a stink about this error that it's tough to forget about it during repeat viewings.