When you come back into the app after some time, the app doesn't open up exactly where you left it off at. You have to re-open the notebook from the shelf and select the page where you were at, the las time around.
This is bug that got introduced with iOS 9.1.2
We are working on this and will be issuing a fix for it in our next release. ETA TBD. Kindly bear with us shortly.