Social Icons displacing on iPhone

The social icons on the top header of my site are supposed to be fixed with the header. But I was able to see an issue when someone scrolls all the way to the top on two different iPhones. In the homepage, there’s some white space at the top and the icons slide upward rather than being fixed on the header. Please note, you’ll have to scroll down first and then scroll all the way to the top to see the issue.