I am having the same problem with this theme on a clean site (no other plug-ins installed).
If you have a top menu item with no sub-items, the navigation works fine – click on the top menu item and it opens.
However, if you add a sub-item to the top menu item, it will not open the top menu item.
You can look here for an example: https://www.newschoolmontessori.com/dev/
Thanks for any support,
Joe