Hamburger Icon disappears on Tablet

Hey everyone,

the Site im working on is this: www.saaman.de

I need some help with the responsive Menu.

I use the Divi Theme and when i switch from desktopview to tabletview my hamburger icon just disappears.

It is the Main Menu, and i tried to fix it several hours but cant get it done.

I already disabled all Plugins, but nothing did happen.

I also found some custom css, but this doesnt seem to be the problem:

.bottom-nav {
text-align: center;
}
body {
overflow-x:hidden;
}

@media only screen and (min-width:981px) and (max-width:1400px){
.cstm_section{
padding-top:100px !important;
}
}

After googleing a lot i think its maybe, that the Hamburger icon only appears at certain pixelrange?!

If You need further Information please tell me.

Thanks a lot in before.