Book document names not updating in Book file listing

I have a book with 25 chapter and 8 appendixes. Suddenly, two of the appendix names in the book file listing won't update, i.e. if I change the first line (formatted as para style Appendix) to something new, the change does not show up in the list of files in the book, it simply remains as it was before the change.

Oddly, if I delete the document from the book, and re-add it, it won't show the title line AT ALL, it just shows the file path, regardless of how I click the title/filepath icon at the bottom of the book listing.

Does anyone know how I can fix this?

Thanks,

- Thom Walker