Product showing on frontend, but not backend

-- url of the page with the problem -- : www.gardengatedecor.com/wild-bird-and-pe...gallon-bucket-holder
-- HikaShop version -- : 3.4.0
-- Joomla version -- : 3.8.7

We have an odd problem. We have found some products that we can get to by going straight to their URL (which we obtained from the database) but they don't show up in the category view nor are they anywhere to be found in the backend. How could a product be in the database, but not in the admin?

By the way... the site is in maintenance mode, so if you need to see the issue in action we will have to send you access credentials. Just let us know where to send them.

We found the issue. The products that were not showing had their category id in the database set to 0. Putting the correct category id fixed it.