Automatic contents not picking titles from all documents in a book

I have been creating a contents automatically in a book.

There are three documents inside the book wrapper.

It was working fine - collecting all the level 1 and 2 headings from all three documents.

Now suddenly its missing the middle doc.

I seem to have tried everything: saved all documents, opened and closed all docs, saved everything, saved the book.

All parargraph styles are set up the same.

Whats going on! Any ideas welcome, my deadline is, well, now!

Thanks