Performance issue

Hi,
thank you for your answer. I’ve tried to create a brand new project. I removed Dynamic sky and I ran the game on a Samsung Galaxy S5 Neo. As a result, at the beginning the fps were 60, but then they went gradually down till 28 in about 2 minutes… It’s like somthing is not working properly here. Can you tell me why? I’m using 4.11 Unreal Engine version. Thanks a lot for your help.
These is a sample video just to show you: DROP FPS 2 - YouTube