How do I fix weird white space blocking text in documents?

I opened a large-ish document (140pp) today, and am experiencing weird white space blocking the text. As shown below, if I toggle "show invisibles" the text appears, but if I turn off invisibles, it all goes blank. Ideas? I tried exporting to word and reimporting but that didn't fix it.

SHOW INVISIBLES ON

SHOW INVISIBLES OFF

It is happening throughout the document.

[Re-Titled by Moderator]