Quote Originally Posted by Dave224 View Post
The problem is in includes/templates/bootstrap/css/stylesheet.css around line 31. I think the following code is intended for mobile only, but I believe the code is applied to both desktop and mobile.
Code:
/* set height of scrollable area in mobile menu */
div#navbarSupportedContent {
    max-height:90vh;
    overflow-y:auto;
}
If I comment out the code, the dropdown slider does not appear.

Dave
I think you've customized the header nav and the mobile nav in a way that combines them into the same div instead of them being separate, else it wouldn't show on desktop mode.