I'm trying to preview an ePub generated with PubCoder Windows version (2.0.3 - 587) on an iPad 3 (iOS 9.1) via wifi.It present the cover on iBooks, but the book is empty. It works with an iPad 3 (iOS 8).
iBooks 9.1 is buggy, happened to me as well several times. Just delete the book on ibooks, close and re-open ibooks and then try again - at some point will work. Hopefully Apple will fix that soon...