The issue can occur when you use multiple notebooks of the exact same type.

 Currently, users can use one notebook of the same type(i.e. N note – pocket) at a given state(You can use different colored notebooks of the same type simultaneously). To enable users to differentiate among them, we have added a ‘Lock’ function which allows users to ‘Lock’ a notebook they were using and create a new notebook of the same type. 

 To ‘Lock’ a notebook, please tap the notebook you want to ‘Lock’ for 2~3 seconds > Tap ‘Lock’ menu. The locked notebook can be seen at your NoteBox. To ‘Unlock’ tap the notebook for 2~3 seconds > Tap ‘Unlock’ and use the notebook again.