Same problem here. Child Theme, responsive/drop-down menu is missing.
I tried from the WP-topbar “customize”, then I tried your way > Wp-Admin > Appeareance > Menus > Set as primary menu.
And still, when the browser width is/goes below 768px, the menu vanishes.
If I switch off from Child Theme and use Generatepress without a child, the dropdown/responsive menu works perfectly :/
What do you reccomend?
Thanks in advance!