My wife has a few files that this is happening to. Somehow, the display cuts of large swaths of text. I suspect it has something to do with when she splits the screen, but have no idea how to fix. The strange thing is, when she opens up the scrivener file in a text reader, all the words appear.
Here are the specs to her Mac:
MacBook Pro 15-inch, Mid 2012
Processor 2.6 Ghz Intel Core i7
Memory 8GB 1600 MHz DDR3
Graphics Intel HD Graphics 4000 1024 MB
Software OS X 10.9.5 (13F1066)
I’m sorry to say that this is a known bug with the Apple PDF reader that we use, which was introduced into OS X a little while ago. It seems only to affect 32-bit applications from my testing, and I have been working on a 64-bit version of Scrivener that I hope will avoid this issue in the future, but that is still some way from being ready.
In the meantime, the workaround is to avoid the use of “Continuous” mode when viewing PDFs (the bug only seems to affect “Continuous” mode, and to instead select View/Media/PDF Display/Page Breaks so that only one page (or set of pages) is shown at once.