Atticus does its best to export your PDF, no matter how you format it. However, there are rarely some scenarios where your content can break this process.
When exporting pdf with many different elements, Atticus may have trouble trying to fit all of your content on the page. Often, this occurs if you are using large images, and Atticus is unable to get these to fit within your other content. This is rare, but often easy to fix.
If this is occurring, go to the chapter which is creating issues, then try changing the size of your images in that chapter to 70% or less. Usually, that will move the image enough for Atticus to properly export the PDF.
If you are still having issues, please write in to our support page here.