When someone goes to order a product on my site and goes through all the steps via PayPal, when they are redirected back to my site they get "Sorry, one or more products are no longer available. Please review your cart"
I am able to replicate the issue. The product still shows as several available.
I have figured out the issue. If an item has several variations like sizes, and one size sells out, this is when the error occurs. So say there are 0 smalls left, and someone tries to buy a medium.