Hi,
I have been experiencing a similar problem.
We've created numerous photobooks over the years in iPhotos and Photos. Unfortunately, with Photos, there is no one button click to create slideshows so based on advice on this forum, we have been using print, save as pdf, converting the pdf's to jpg's using Automator, importing those jpg's back into Photos and then creeating a slideshow. It worked for the first slideshow (most recent project) but when I started going back to past Photos projects to repeat the process, when I print to pdf, i keep getting one or more (up to nearly 10) missing pages in the pdf. The pages are still missing if I exit Photos and try again. I've also tried the preview print mentioned in this thread - and the result is even worse, after 5 or 6 attempts, each time, I only get a pdf of the cover page without the picture, just text.
Can anyone guess what the problem is? It is such a pleasure to view photobooks as slideshows, especially when sharing with friends and family. While hugely inconvenient, the workaround was an adequate compromise until the pdf conversion started failing. I've tried this with 4-5 past projects now, and have not been able to produce a 100% intact pdf with any of them.
Any help most gratefully received!
Chi Wai