Zerif-lite child theme

I have the following theme installed with a child theme .
When I open the menu and exits directly , it works perfectly.

But when I scroll down a bit when the menu is open and close the menu, then the box get stuck until I scroll at the top again, then the box resize again.

the wierd thing is that it works on the desktop when i resize my window. It′s just on iphone and android it won′t work. try if you want at Studentsmart.se (password: test)

Link to printscreen