Hey Silvan,

Be sure to uncheck the Off Canvas Menu Mobile Nav Menu items [This will cause your off canvas menu to inherit any navigation items assigned in your "Top Navigation" menu location when viewing on a mobile device]

in here : 

Bes.t

Hey Again,

If you want a Different Menu for Mobile . Turn off the Inherit Option and Add a Custom menu in the Off Canvas Widget Area . 

Hey Again,

Now make sure there is no menu selected in here : 

Hey Again,

Add this into the Custom CSS box located in your Salient Options panel (Make Sure there are no red cross in the Box) :

@media only screen and (max-width: 1000px) and (min-width: 1px) {
    #slide-out-widget-area.fullscreen .inner .off-canvas-menu-container, #slide-out-widget-area.fullscreen-alt .inner .off-canvas-menu-container {
        display: none !important;
    }
}

Thanks

Just added in additional css . 

@media only screen and (max-width: 1000px) and (min-width: 1px) {
    #slide-out-widget-area.fullscreen .inner .off-canvas-menu-container, #slide-out-widget-area.fullscreen-alt .inner .off-canvas-menu-container {
        display: none !important;
    }
}

@media only screen and (min-width: 1000px) {
    #slide-out-widget-area.fullscreen-alt .inner .widget {
        display: none !important;
    }
}

Please check now. 

Thanks

Add this into the Custom CSS box located in your Salient Options panel (Make Sure there are no red cross in the Box) :

#slide-out-widget-area.fullscreen-alt .inner .widget.widget_nav_menu li a {
    font-size: 30px;
    line-height: 30px;
    font-family: 'Open Sans';
    font-weight: 700;
    letter-spacing: -1px;
}

Thanks