This is caused by optimizations of the WebView (which we use for rendering) on Android 5.
To resolve the issue please update the Android OS on your device (firmware update).
Once this is complete please then update the Ebook Reader app. This should then resolve the white space issue.
If you are still experiencing the same issue please contact our support team. Please state what version of Android you have installed on your device, and what version of the Ebook Reader app you have installed.