Buffer breaks on very large files

At least, I assume it’s very large files. I imported the ebook version of Dune in order to do some cleanup—202472 words, 1166323 characters—and it displays it fine, and scrolls fine, but any changes are not reflected. I type in it, and the text displayed doesn’t change at all—though the word count does. I do a Find or Find and Replace for any char, and it jumps to arbitrary characters that don’t correspond at all.

I just select-all’ed and deleted, to see if I could get the window back. Scrolling revealed empty space on both sides (though the buffer displayed didn’t change), and the word count went to 0, but after a second the whole app crashed. I’ve got the crashdump txt.

Please send me this project IMMEDIATELY. I have heard of something similar but have never reproduced it. Please send it to support@literatureandlatte.com. Without the project, I can do nothing to help. I have tested Scrivener with 300,000 words and more without issues, so I really do need a project that causes problems.
Thank you,
Keith