Out of Stock if you're not logged in

We are experiencing an issue where products can't be added to a cart (inventory on or off) if the user is not logged in. I can't seem to figure out how to fix it.

Here is an example. http://storeexample.digitalpto.com/

Try adding something to your cart. Say's it's added and then it changes to out of stock. I have some items that I've tried to add stock to and some that have no settings, they all do the same thing if you're not logged in.
Using V 2.1.2

Thanks so much

Matt