Hello,

Sorry for the late reply.
This is not an issue of sticky header. This is the sticky style of the header you have chosen. To include the menu too, in sticky header, you should edit the css.
Let us know if you need help.

Best regards!

Hello,

Sorry for the late reply.
I added this code into your custom css box(test site):

.sticky_header .full_nav_menu {
    position: fixed !important;
    top: 112px !important;
    visibility: visible;
}

Please check your site and let us know.

Best regards!