InDesign freezes on export to epub

I've been fighting with this for several days now.

I have a book of approximately 200 pages with some images. I use two Adobe fonts and various style sheets and character styles (for bold and italics).

I've output the book to PDF with no problem.

When I try to output it to epub, it freezes. The balloon spins endlessly, and the Activity Monitor shows the CPU usage going to 100.3%, and then it says InDesign (not responding).

I have tried the following fixes (not necessarily in this order):

1. Replace images with low-res images.
2. Remove images entirely
3. Remove paragraph styles
4. Remove character styles
5. Remove master pages
6. Remove all fonts other than Arial
7. Delete InDesign preferences.
8. Checked my hard drive for errors.
9. Change the Export settings.
10. Change the Object Export Options.
11. I exported the book, starting with only the title page and going up chapter by chapter. When I arrived at Chapter 6, it stopped. Other chapters beyond that hung up also. I started working with a copy of chapter 6 only. I finally got it to work when I deleted all the text and replaced it with a couple of progress of lorem ipsum.
12. I put the original Word file I was working with into a document, unedited, and it worked.

I'm using a MacBook Pro (2015), OS 10.13.6. Adobe InDesign 13.1. The images are line art and photos, and I've tried both JPG and PNG without success. I placed them inline in the text. The fonts are some I accessed through Typekit. But the same problems persist when I use just Arial.

It seems that there's some problem with the text itself, but I'm at a loss how to troubleshoot it. (Oh, and I also removed the forced line breaks in the Export menu.)

Thanks for your help.