I have more information. The issue happens when the Product Order By is not “Date Created”.

The issue is reproducible in a fresh Quickstart install (contains sample data) of the theme:

1. In the frontend, you can see that the first product in the SNS tabs is “Stablished fact reader”. The SNS Product Tabs shows 8 products.
2. In admin, go to SNS Product Tabs
3. Under Filter Options, set Product Order By = Price
4. Now edit the product “Stablished fact reader”:
Manage Inventory = Yes
Qty = 0
Stock Availability = Out of Stock
5. Go to frontend, you will see an empty spot. SNS Product Tabs only shows 7 products. “Stablished fact reader” is missing.