The problem you experienced is not showing in video. Try to shoot the video using second phone as it will not be visible on screen recording.
From your message, it looks like "display burn-in" it happens when you use any app for much longer period in full brightness. The still parts of the app (like headings, design of app logo) is displayed even after closing the app.
Don't worry. Try to cool down the phone, reduce the brightness or lock the phone for some time it will go away as it's LCD display. Display burn in in LCDs are not permanent
