I posted about this a few years ago but this problem remains unfixed.
I regularly make large "Blurb Photo Book"s in the LR Book Module that bump up against the 440 page limit using standard paper. I also have really lousy internet. I sometimes have to print a "PDF" book to a thumbdrive to upload at a different location with faster internet. This works well.
The problem occurs when I want to switch back to a "Blurb Photo Book" from "PDF" in the Book Module. I get the following error message:
Clearly this is a serious problem for me and one I dont dare try to experiment with to work around. I believe it would not be difficult to set the Blurb Photo Book paper to "standard" paper to avoid this problem.
Updates to the Adobe Photography Products were released today and contain a fix for this issue. Please install the update via your Creative Cloud Desktop App or your respective App Store. Note: You may need to refresh the Creative Cloud App for desktop software to show an update available. ([Ctrl/Cmd]+[Alt/Opt]+ [ R ]) For Mobile downloads, it may take several days for the update to appear in your respective App Stores. Thank you for your patience.