Happened in the past to us that folio was messed-up on server - it was possible to see it and modifie in Folio Builder, but didn't shown in Viewer on iPad. I would recomend to create new folio just with one blank page for test, if you will see this folio on iPad 1.
I am not sure exactly what happened. One of the articles imported, but it wqas scaled down 50%. Due to the size difference it would not load to the Viewer.
Reloading into the Folio did not work. I created another Folio with that article, loaded it. Then I copied from one folio to another in the Folio Producer.