Issue: A drop down menu only displays sub-menus on the page it links to.
Solution: If there are no JavaScript errors and the arrow next to the drop down menu is not displaying except for the page that menu item directs to, be sure to visit the menu section in the Drupal settings and check of “expanded” next to that menu item.
Not that I’m sure this is needed, but clearing the menu cache (using the admin menu module) might be a good step to take as well.