Customer got Out of Stock error, but no stock limit is set

[RS4]

Hi,  I had a customer place an order on our website and they received an out of stock error. It didn't tell them what was out of stock.  The strange thing is that we don't have stock set for our items. They came in and placed the order in person and told us about it.  Is there a setting or something that could cause this error?

[goldburger]

this started happening out of nowhere to only one item. support said the have no immediate fix for this bug. ¯\_(ツ)_/¯