MyListing hides icons on submenu links in the default MyListing header, even when you assign them in Appearance → Menus. That makes nested items harder to scan and wastes work you already did on menu icons.
The code snippet below reveals the icons.
CSS
/* DESKTOP */
.main-nav li a>i {
display: inline;
}
/* MOBILE */
.mobile-menu-open .i-dropdown li a i {
display: inline;
}