How to reset caches?
Once in a while, the cache might not be updated properly which results in old data being displayed (like on iOS the overdue number is higher than the actual overdue tasks or notes and folders that exist in the sidebar but not on your device). You can fix this by resetting the caches.
On Mac
In the menubar under "Help" select "Reset Caches":
On iOS
Open the NotePlan preferences and scroll to the bottom: