Sticky header works properly on our theme, I just tested it on my computer.
When I visit your site, I saw one error. Please see screenshot. http://prntscr.com/7fmz3f
Maybe that is what’s causing this issue.
You are advised to disable one plugin at a time to see which one is causing conflict. Reload your browser when you are doing this trouble shooting.
At the moment you can use this following css fix to hide your sticky menu.
In Theme Options-> Custom CSS Please use the following.
display: none !important;