Here is the screencast using your theme’s sample data, “Stablished Fact Reader” (this is example only for proof of the bug, your actual theme may have other product than “Stablished Fact Reader”): http://screencast.com/t/nVOoK6VFX1

You will see that the item was out of stock and is causing bug on the SNS Product Tabs (missing item, showing 7 items instead of 8).

After it was set to in stock, the item can be seen in the SNS Product Tabs (showing 8 items which is correct).