Hi. I have a long time experience in obtaining Blurb books from Lightroom. In the last week I have experienced significant problems and have contacted Blurb who have washed their hands of the situation and advised me to contact Adobe directly. Last week I was, after many hours, able to upload a book to Blurb - during this exercise I had to repeatedly monitor the process and press the resume option on the displayed error dialog. The book is now being printed. Since this is coming up to Christmas I wanted to upload a smaller size book (for presents) using the same layout of photos. This time following the same procedure (hitting the resume button repeatedly) and after 6 hours or so the uploading would not complete. In all cases the progress bar reaches around 50-60% in a reasonable period before the error message starts to be displayed.
On Blurb's recommendation (their standard response) I tried to create a PDF of the smaller book size only to be immediately confronted with an error message shown on the screenshot below. At Blurbs suggestion in Photoshop I soft proofed the original PSD's using the Blurb ICC colour profile and saved the images as high quality jpegs.
I'm having exactly the same problem: and also with LR Classic CC 8.0 & Mac OS 10.14.1. Trying to upload a book to Blurb (110 images, all NEFs or JPEGs, all RGB/sRGB, none enormous). I can make a trial PDF version ok (though no book cover of course). On main Blurb book upload it renders ok, then starts a steady stream of "There was an error uploading your book" messages every couple of minutes (I click "Retry Upload" every time). Then after 3 hours of this its crept up to about 70% on the progress bar and then these messages start coming in every few seconds. I.e. the upload has hit a brick wall. I've tried this several times, changing things like formats (a few images were TIFs initially) and image size but it fails every time and always in the same way. I've been at this for two days now..... aaaaaargh!
Blurb say "Not us, we're just printers, ask Adobe".
Did your change work (soft proofed the original PSD's using the Blurb ICC colour profile and saved the images as high quality jpegs)? I.e. did it then upload & print ok?