Did you ever figure out why Lightroom was doing this? I am having the same problem with any edits I made to my book...
Are you making a "Saved Book" Collection? This is the best way to preserve any edits to a book.
Use the same font throughout the book - (suggested, as some complain the book cannot be sent to Blurb or PDF with many fonts)
Use the following method and check if your text is preserved.
1. Start the book initial design
2. Click the tab [Create Saved Book]
3. If you return to the Library grid, or close Lightroom down, always re-open the Book from the Collections panel, to continue with its design.
4. Click on the white ARROW to re-open the saved book in the Book module.
Clicking on the book NAME in the collection panel will only show the grid of images available to the book (you can add more images to this collection)
"Book" collections work like "Smart Collections" as they record and remember everything you do when you edit the book.
I really appreciate your help. I tried clicking on the white arrow (I hadn't even realized that was there!) and it still didn't work. The weird thing is that it saves my work when I am working on other saved books, but just not this one.
Have you tried to copy the book and then edit with the copy?
TO copy a book- Right-click on the Book Collection name and choose "Duplicate Book". Edit the 'copy' from the white arrow.
Also try resetting all text fonts- (you could try this on a duplicate book! )
1. press [ CTRL+ALT+A ] to select all text in the book. (Menu > Edit > Select all text cells)
2. In the Type Panel select a common font and suitable options for size.