Book Module - Pages 40 to 61 of my book disappeared and cannot be recreated

I created and saved a 61 page book in the Book Module and even exported to a PDF.  Several days later when I was making edits to the book, all the pages from 40 to 61 "disappeared". The film strip shows the pictures are in the book but the pages are not visible. When I add new pages with the photos, they are visible but as soon as I move to Library Module or exit Lightroom Classic, the new pages disappear. The film strip shows that the added pictures have been now used twice but the book ends at page 39.

I have tried creating a duplicate collection and completing it with pages 40 to 61 but it also stops at page 39. 

This is my 20th book created with the Book Module and published on Blurb and nothing like this has every happened before.

Could someone please help me ?