Help! Jumping menu problem

Hello there,

This is my site.

I use sticky header for my menu. When the page is scrolled down, the menu is on the right position (the position I want). But when the header is on the top, the menu moves to the left, not on the correct position.

I used the exact same code once before, but they work differently. I can’t find out why. Is there some one can help? Thank you in advance.