This happens when you have enabled "Automatic Stock Control" but did not upload the stock file.

More importantly, ALL Products in your shop must have unique Catalog Number

- Open your shop in ShopFactory

- At the left tree menu, click on the LIST of Contents

- Check all your products have unique catalog number/ item number.

- If your products have OPTIONS and CHOICES, then make sure you also go into the Product dialog -> More... -> Options and Choices and assign unique catalog number for each choice.

Once you have completed the above, tick "Enable automatic updates of stock levels" under Services menu. 

https://shopfactory.deskpro.com/en-GB/kb/articles/en-automatic-realtime-stock-control

You need to publish the stock file again via Central -> Stock Levels dialog.

NOTE: Please make sure that your Publish SETUP dialog box contains your correct hosting details. ShopFactory uses the details in the publish setup dialog to connect to your Host.