This is something I haven't noticed in previous versions.
In a 323 page 6"x9" document, the main window scrollbar only takes me as far down as (physical) pages 286/287. Never past that.
If I use the left-hand Pages display to scroll to the bottom of the document, the main window scrolling behaves as expected from that point onward.
And yes, I have waited a while to see if it clears up, i.e. the program is busy computing something.
This happens on two computers.
Windows 10 - 64-bit