Not My Canon!

WTF: Exposition

The butterfly effect is the phenomenon whereby a minute localized change in a complex system can have large effects elsewhere.

Something is Different

EXPOSITION, as a way in which to explain the current situation in the story to both the reader and to those within a given scene, is necessary. Such a thing is twofold in cases where time travel is the main plot device, and threefold when they deal in "butterfly effect" scenarios, wherein the protagonist returns from their adventures to realize that they inadvertently caused the present to change.

This requires a good deal of dialogue to be exchanged between characters, as they discuss why things are different in this alternate reality. There are explanations of how one or more characters have evolved or devolved, and what can be done to return things to normal.

If you want to tell this kind of story, you will come to see this exposition as an essential part of your hero's experience. Unfortunately, Cursed Child goes back and forth many times and experiences multiple versions of the same character, which led to an exhausting amount of reiteration for the reader. But the nature of the story they chose to tell makes this almost inescapable, which is unfortunate. Although the audience knows what has happened and don't need it explained a second or third time, the characters in the scene DO need to understand because NOTHING MAKES SENSE.

Sheesh...no wonder Cursed Child had to be more than a one-night event! Honestly, this should have been limited to one scene. And if the story didn't lend itself to that, then they should have made their story work differently so the readers wouldn't have had to sit through multiple exchanges of long exposition.

Ron reacting numerous times to the fact that he was (or was not) married to Hermione became tired. We don't need this. There is so much pointless fat in the play that could've been cut. If you're honestly going to create two plays, keep this part of the process lean and use the time you have remaining to elevate the story and add complexity instead of chaos.

Too Late To Fix

In many ways, they shot themselves in the foot with this story concept and there was not much they could do to escape the need to regurgitate the same spiel over and over again. Sure, we can use it as an excuse to have Ron suggest renewing his vows to Hermione, but it doesn't change the fact that an unnecessary amount of time was devoted to exposition.

And it's not as if they weren't self-aware. There are times when the writers used their own dialogue to set the reader's mind at ease:

GINNY: Haven't we been here before?

HARRY: Something feels even worse this time.

No, I'd Like An Answer

Worse was when the characters needed and deserved a bit of exposition to comprehend the absurdity of their current situation, and the writers brushed past it. Like in Act Four, when the adults arrived in the past and Scorpius, who always seems to say what the reader is thinking, tries to understand.

SCORPIUS: How did you - how did you, without the Time-Turner -

HARRY: That's a long and complicated story, Scorpius. And we don't have time for it.

Mmm, it's actually not that complicated.

Your dad had a second one.

Done.

Oh, that sounds super ridiculous now that we say it out loud?

We just... brought out a... second... one...

that has better powers, by the way...

the moment our protagonists were in peril...

and it was desperately needed in the story...

Maybe we just have Harry say it was "complicated". It's also the end of day two of this play and people are getting tired and it would leave a huge loose end with the whole Was Voldemort My Time Travel Daddy? deal with Scorpius, so... No time to discuss it, just move on. Yep, WAY too complicated.

*blinking in silent indignation*

This is all a prime example of overwriting. Not in the flowery, "Kill Your Darlings" sense of the word (which they did as well). No, this play was written with reckless abandon. JKR and Co. knew that they could make the play a two-night event a three-night event if they chose to do so. The audience would be there no matter what. So, they allowed the plot to become so convoluted that it necessitated a need to be explained more than once.

This style of writing is lazy and ignores the value of monitoring the word count; of paring down your story until it is the grandest it could be in the fewest number of pages possible.