Swipe from the bottom of the phone to view the home...etc

[AC Question]

Brand new Galaxy S8+. When I turn the phone landscape or hit full screen on YouTube or any other video player the screen goes half gray and this super annoying prompt comes up and won't go away until I back out completely "Swipe from the bottom of the phone to view the home, back, and resents buttons" And doing what it asks gets no reaction. It just stays until I turn the phone back to portrait orientation.