Hi,
All the possible causes which could lead to that are listed in that FAQ:
www.hikashop.com/en/support/documentatio...or.html#notification
Please review each point and you should find why the orders are not confirmed.
Looking at the information you already provided, there is a high chance that it comes from that point:
Your HikaShop menus have not the access level public. Because of that PayPal servers cannot access your shop to notify HikaShop from the payment. You should configure the "force a menu on checkout" option of the configuration to a public menu that while your categories/products listings are not accessible to your users, PayPal will be able to notify HikaShop.