black screen at fullScrren mode

I have a game with a button that changes the status of the screen to "Full Screen"

Everything works fine, I can enter a state of "full screen" and go back many times, also when there is background video, I can enter a state of "full screen" and see the big video.

But there is a problem, after I complete Treatise with video in and out. Since then, every time I go into a state of "full screen", whether video background or not, the entire screen appears black.

Clearly the fact that the video was in "full screen" status, is the cause

How can I Prevent it? specially the target is to see also the video on full screen status?

Thanks all!