In LR 6.6.1, I prepared a 67-page book using the standard layout pages to add photos and text. I used Myriad Pro font for the standard-layout text boxes. Myriad Pro was also used for the added page-text boxes, and none of these added page-text boxes overlapped with the photo cells.
However, I always get the error message "An error occurred when adding text and fonts to the book" when either trying to "Export to pdf" or "Export to Blurb". Curiously, the cover always saves into a separate file. But the content never saves into the second file (that is expected).
This seems to be an ongoing problem in the Forum. For my problem, none of the suggested solutions have worked. For example,it does not work to select all text cells, then do a global font change.
Advice to fix this problem will be appreciated. Preparation of books is a useful functionality that worked well and predictably for my older LR 4. Updating to LR 6.6.1 seems to have reduced the functionality of LR !
However, I always get the error message "An error occurred when adding text and fonts to the book" when either trying to "Export to pdf" or "Export to Blurb"
Also, you can update the Lightroom to the latest update available 6.9 and check if that helps.