I've been given a 20 page document to edit by swapping four of the pages. They all worked fine but someone noticed that when you clicked on one of the pages it reduced in size compared to the rest.

But it then has a knock on effect of keeping certain pages smaller so you'll be flicking through the document with some pages at 66%, then all of a sudden another page will bring the pdf back to 100%.

I've checked and the pages are all the same dimension size, and the scale view definitely goes from 100% to 66% so it's not just a case of a smaller page(s) being inserted.

Doe this make sense to anyone?

Is there any setting I could have overlooked that might cause this, as I didn't make the original file it may have been missed?