There are two reasons you might have blank pages in your exported PDF document.
When a page or chapter is set to start on the right side of a book (ex. first chapter of the main content) but the previous page or chapter also ended on a right side page, Atticus will automatically add the required blank page on the left side so that the next chapter starts on the right. (You can learn more about that here.)
We recently updated our PDF generation system and the transition has caused some books to include blank pages where they are not needed. For these the blank pages, you’ll just need to do a bit of a reset to fix them: click the three dots next to “Body” in your content list to reset the “Begin on” settings, selecting something different than you have. Then leave that list, click back into it, and set it back to your preferred setting. You only need to do this once after you’ve updated to the new PDF system.