Mobile Menu bar not showing up

Hi there... I've perused the threads here and can't find anything that quite helps. The menu bar on mobile devices (iPhone as well as Android) does not show up. I have that option enabled in the theme settings. Every once and while, I'll see it. But as soon as I refresh, it's gone. I don't have any plug-ins enabled. https://www.ccboe.com/sciencecenter/ Thank you!