The second time Scorpius and Albus use the time turner, they do so to humiliate Cedric in the second task. He's so upset, he becomes a death eater and kills Neville Longbottom at the Battle of Hogwarts so Neville never kills Nagini. Apparently, this one change means that Harry dies at the Battle of Hogwarts. But really - this doesn't make sense, does it? Neville killed Nagini after Harry "died" in canon. Anyone could kill Nagini to do the job. Harry is "killed" at the Battle of Hogwarts but is tied to life because Voldemort used Harry's blood in GoF. Really, they either needed to have someone else (could be Cedric) kill Harry (because Voldemort had to be the one to kill Harry for the "tie" to work) or stop Voldemort using Harry's blood so he wasn't tied to life as well as Neville dying. Nor does it explain why Snape is alive in the alternate universe if Harry dies "on time" as Snape was already dead at that point.




Honestly, I guess it is better not to think too much of the lot or else we will find many other plot holes. It feels like Thorne and the gang haven't really invested that much time to create an amazing story, not nearly as much as the play itself. It's like they thought "play will look brilliant, i'm sure no one will mind or even notice the inconsistency".