Here is why you might have blank pages appearing between uploads in your notebook.
1) Why Do Blank Pages Appear?
When you first enter your Room you will be presented with the current page of your notebook. You can check this by clicking on the (?) in your toolbar.
When you click the forward arrow you either move on to the next page or you create a new page. If you were on page 5/12 when you clicked the forward arrow, you will move to page 6/12. If you were on page 12/12, you will move to page 13/13. Whenever you upload a PDF it will be shared on a new page in the notebook. If you were on page 5/12 when you upload a PDF, the PDF will appear on page 13 which may leave some blank pages between page 5 and page 13.
2) Filling In The Blanks
Blank pages are not a problem but if you'd like to fill them up you can do so either by drawing/typing in them or by sharing an image.
Sharing images works differently to sharing PDFs. Images are uploaded onto your current page rather than a new page.