screen goes off in youtube app

[AC Question]

Greetings,

I have a Huawei P9,

everytime I use the Youtube App only, and turn my phone sideways to landscape, the screen goes blank and the the phone locks.

same when i put fullscreen on a youtube video, full videos go to landscape automaticaly, same thing, blank screen - phone locks.

i tried every possible phone setting (autorotate on-off, brightness etc) nothing helps