Note8 and youtube in smaller window

[Vill-vapes]

Everytime I'm watching youtube my note8 keeps making the window smaller no matter how many times I make it bigger it keeps shrinking it how do I stop it from happening

 

[B. Diddy]

Welcome to Android Central! Is it becoming Picture-in-Picture? Do you see the main YouTube screen in the background, or does it exit to the homescreen?