Hi,
Did you check that their configuration is identical ? Because if you duplicate the menu items, the HikaShop settings might not be duplicated if the source menu item was setup with an old version of HikaShop where the settings were stored in the HikaShop configuration and not in the menu item itself.
Otherwise, fi the menu items are really identical, then the problem is with the products themselves. For example, they don't have stock, or they don't have prices, or they're unpublished, etc. So please check the products.
It's either coming from the products settings or the menu item settings. I don't see any other possibility.