Can't scroll to top, it stuck in middle.

[gursewak-sohi]

When menu item is clicked, the page scroll to some position, but cannot scroll to top position again, it stuck in middle.
Example:-
<a href="#aboutUs">About Us</a>

<section id="aboutUs">...</section>

when about us link is clicked, it takes the position to section About Us. But i can't scroll to top again. it stuck

I found something related to the issue.
#128 and https://jsbin.com/jequfuq/edit

This works only inside the page, not for whole page.