I follow this video tutorial.
I check my source code with the GitHub example and is similar in most part.

That GitHub example theme named Aquila works on my WordPress install.

My WordPress test area is installed into localhost.

The implementation of the menu: class-menus.php works and the menu is shown.

The problem is the dropdown effect because the menu is frozen with the WordPress theme and not show all items menu.

If I click on the first menu button I got this:

The requested URL was not found on this server.

I think the problem is this part of the source code build by nav.php file and bootstrap files :

id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">