Top Menu Behavior doesn't make senseBrowser Info Environment
The theme uses a standard Bootstrap menu, which has a non-navigable parent menu item if there are children items, for mobile accessibility. If you have "About Us" with children items, the "About Us" will just be a placeholder so when the user clicks on it this will open the submenu items. If you want the "About Us" page to be navigable, then you need to make the submenu items non-navigable by choosing "exclude from nav" in attributes.
As you can see from this demo http://cariad.pilipalawebdesign.com/... the parent items with submenus are non-navigable pages.
There are various workarounds if you have a client who requires the top item to be navigable. If you google "Bootstrap navigable parent" or similar, you will find a few. This is my favourite one so far https://github.com/mrhanlon/twbs-dropdown-doubletap,... but I haven't tried it with that theme and it would require advanced knowledge to implement. If you do change any theme files, please make sure you keep a copy of the modified theme files elsewhere so you can upload them if you update the theme in future, as updates will overwrite any changes you make.