How I fixed the position on top of website ?

Hello I have a problem on my site and wanted to know if they can help me solve. I created a split at the top of my site to accommodate three 'divs' and put two instances of toggles buttons using a plugin that calls ShiftNav menu. When the site is accessed, it is perfectly aligned with the top edge. When I go up or go down the page, the menu I created is fixed. However, if you are in the page scrolled down a bit, and I click the button, the menu disappears and goes to the top of the page until I close the sidebar. This has something to do with the plugin? If so, no way to fix it independende page position, when I click on the buttons? Thank you Website address