Browser cache problem
If your menu doesn't work as it should be, but if you press Ctrl + F5 (hard refresh), it's working, that is because the browser is caching down some bad data. This can happen, when the Joomla cache is turned on, and in the Extensions → Plugin Manager → System – Cache → Use Browser Caching is turned on. It's usually working with out menus, but it can trigger an error in another extension, or in the template, which affects our code. You should just turn it off, it doesn't really give that much extra speed.