Not everyone who loves the Marvel Cinematic Universe thinks that Avengers: Endgame is a perfect movie, as much as it exceeded all expectations in box office totals. The biggest problems still occur in fan opinion of the time-travel heist and how many plot holes exist therein.
No one can do time-travel like the Russos attempted without having a few things not quite stand up to scrutiny. While some still argue time-travel rules set forth in Endgame made sense for the Marvel universe, others think it created extra and needless confusion.
Who is really right here? The place to start is with fan opinion on social media where trying to figure out the time-travel complications is like dissecting a complicated physics equation.