The Drupal menu system requires a page to “live” in a specific place in the navigation. Unless it’s a top-level navigation item, it will have a specific parent and if it has sub-navigation items, they are its’ child navigation items.
There are good reasons to want to put an item in two different areas of the website navigation. But you still want it to show the the right sub-navigation and live in the right area of the site. Sometimes Drupal won’t cooperate. No matter what you do, how many times you set and re-set the menu items, for some reason it will not display in the right hierarchy.
Solution: For the additional menu item, the one you want to take the visitor to the other area of the site, add it with an path that is the absolute url in the Main Menu Navigation interface. Absolute paths, include the the “https://” and root part of the address.
Normally, we want to avoid absolute paths to other pages within the same site. On the test version of the site these will link to the live site. We have actually thought we were on the test site and done some test work because we clicked on a path that took us to the live site and we didn’t realize it. Also, if the root url for the site ever changes this link will be broken.