Mobile Menu not sticky

Hi there!
I wanted to try to build a quick website with this template, but I think I found a bug.

For some reason the header is sticky on the desktop version, but when viewed on mobile, it wont stay in view.

Also whats the differenceb between the normal mobile menu, and the "alternate" version? I don't seem to find any differences.
thats the link to the work in progress in site:

http://www.snckrz.bplaced.net/pflegesaarland/

Nevermind, found someone else having the problem here:
adding sticky-responsive-menu as a body class solved it