I've got it working.
Perhaps the problem was the numbered list used in the Chapter Title paragraph style? I had said to convert numbered lists to text in the ePub Export dialog.
Some combination of these steps solved the problem in case others encounter the same thing:
a) Changed the chapter headings using the Chapter Title paragraph style to Chapter Title FM. This style does not used a numbered list. Of course, I had to manually type "Chapter 1" - before each chapter title.
b) Once all occurences of the Chapter Title paragraph style were gone, I redefined the TOC definition to remove Chapter Title. This leaves me with a single Level 1 and a single Level 2.
c) Updated the TOC with the new definition.
d) Moved the TOC frame from the pasteboard to some blank space in the front matter. I did not bother to make the frame large enough for all the text, since InDesign will delete this upon export.
e) Export to PDF. On the third panel, changed the "break at: Chapter Title" to "break at: Chapter Title FM"
My theory is getting rid of the numbered list in the chapter paragraph styles probably solved the problem. Thanks to all who took the time to check out the discussion.