Web Store Items Displays Out-Of-Stock even if there are Stocks On Hand And Available

This applies to accounts that have Multi-Location Inventory enabled. The feature can be found in Setup> Company> Enable Features> Items and Inventory tab. The Web Store Out Of Stock Items preference in the Web Store Set Up and Item Record controls the behavior.

Make sure that you have the following enabled on the location record:

1. Navigate to Setup> Company> Locations
2. Edit a Location record
3. Put a tick on Make Inventory Available in Web Store
4. Click Save

Note:
If the preference is not enabled, items from the location will only display the out-of-stock message.