It din't work all the way down the sub-menus but I managed to adapt the code to work... Following your line of thinking, I added 5th and 6th navigation levels...
/*off-canvas issue*/
.t4-offcanvas .t4-off-canvas-body .mod-menu-flex .drilldown-effect .navbar-nav .dropdown-menu {
top: 0;
transform: none;
}
.t4-offcanvas.oc-level-3 .drilldown-effect .navbar-nav {
transform: translateX(-300%);
}
.t4-offcanvas.oc-level-4 .drilldown-effect .navbar-nav {
transform: translateX(-400%);
}
.t4-offcanvas.oc-level-5 .drilldown-effect .navbar-nav {
transform: translateX(-500%);
}
.t4-offcanvas.oc-level-6 .drilldown-effect .navbar-nav {
transform: translateX(-600%);
}
.t4-offcanvas .t4-off-canvas-body .navbar.drilldown-effect .navbar-nav .nav-item {
position: static;
transform: none;
}
Thank you!