This is happening to me in Feb 2019 on iOS SE 12.1.2 - even when there is no notification and no messages in inbox, the little red notification badge still appears over the app icon on my home screen. When I go into the app, the notification badge shows over the notification tab, but when I open that tab it realised there is nothing there and the badge inside the app disappears. However in closing the app the badge on my home screen remains.
