The easiest way I can explain my problem is that there is a transparent screen of icons and widgets from the default note 4 home page that still shows while other apps are running.
I tried screenshotting but for some reason, the bug doesn't show on the screenshotted pictures. So here is a picture of the bug that I took from another phone. You can see even on the camera app that there is a glimpse of a homescreen with the calendar icon showing (31).
That is screen burn-in, which is common on phones with AMOLED screens like the Note 4. This is usually able to be lessened by displaying a white image on the screen for a few hours. If this doesn't work, the only way to completely get rid of the burn-in is to have the screen replaced.