Membership plugin removes drop-down menu structure in Scholar theme

I’m using the Scholar theme with BuddyPress and have installed and set up the Membership plugin. When I’m logged in as a member, all is fine but when I log out and become a visitor (with visitor/stranger set to Free Level), all my drop-down menus cease to be drop-downs and instead I get 2 rows of my 1st 20 menu items instead.

How can I retain my drop-down menu structure for visitors?