Admob auto close in note9, note 8

Hi, my admob ads are acting funny. They just auto close them self. At first they pup up as it should but automatically closes it self just after opening. But I have not change any code, it started to happen around 2 weeks ago. It was working just fine but all of my playstore app suffers from this not just one.
But i heard from the user, it is auto closing in note 9,note 8 but shows ads on s7 edge, Redmi note 4…

This is my one app

Why ads are auto closing?