We are also having this problem. The stock number is set to infinity, the product is enabled. The products were added to a page with the product module in the page editor - there are no disabled store pages that have those products. I just disable express checkout, (which we had wanted to use for service products) and disabling that didn't help.
Why can we not add physical products to cart or checkout?
https://www.greenpathherbschool.com/swag