Shaky scroll – sticky disabled as default?

Hi all,

Somehow when I scroll slowly, the screen shakes somehow untill you get over a certain point.
It seems to be that “sticky-disabled” is set as default, instead of enabled even tho I’ve set the menu as sticky.

class="page-template-default page page-id-1840 logged-in admin-bar table-layout tc-fade-hover-links tc-no-sidebar tc-center-images skin-black tc-sticky-header tc-transparent-on-scroll tc-regular-menu customize-support wpmm_megamenu woocommerce chrome tc-smoothscroll sticky-disabled"

Anyone any idea how to set sticky-enabled as default?

The page I need help with: [log in to see the link]