I made it work with FCP
I had been AB testing this all day. I was starting to think that it had something to do with the limit of chapter markers. I deleted most of the content and tested different numbers of chapter markers, I was between 29 and 31 when I started getting inconsistent results.
I found another thread from a few years back where someone else was having the same issue until they removed a random ‘&’ in one of the chapter titles. I went back and found that I had hit Enter/Return, and there was a second line of text hidden below. I removed that, and put it on one line, and to my surprise it exported with the menu.
Finally I attempted exporting the original 2 hour project, with out the Enter/Return Space in that one particular chapter marker and CONFIRMED: Removing the unintentional Enter Space resulted in the 2 hour show with 36 chapter markers, exporting successfully with a Table Of Contents.
Who would have thunk it?!