Notification centre widgets not working

Hello everyone, i am an experienced Apple user and I cannot find why this is happening. My calendar notification centre widget, is folded up. It only displays the top bit calendar app icon and 'Calendar'. I have tried a restart, tried flipping through the calendar app to make the widget respond but it doesn't work. I've had similar problems with other apps from the App Store so I just delete and reinstall however you cannot do that for calendars. Please help me and thank you for taking the time to do so.