If you right click over your window and select 'Display Settings' then on Notifications and actions you'll get lots of options for notifications and see what programs (or apps as they are apparently called nowadays) are sending you notifications. I notice this with Discord; if I get a notification pop up from any of the channels I monitor then it overlays the bottom right of the screen. Sometimes if I get a lot of notifications all at once although the actual notification isn't showing the area will be sort of waiting for text to pop up and this prevents me from accessing that part of the screen.
