Hi,
we have just noticed that some variable products can no longer be placed in the shopping cart. If variables for color and size are selected, a popup appear with the message “Unfortunately, there are no products of your choice. Please choose another combination”.
The error seems to occur after the theme update (from 3.8.x. to 4.0.2) for all products for which we have not generated a variant for each product variable in the admin. (Some of our products would generate hundreds of variables.)
So far, however, it has worked.
We have deactivated the stock management at WooCommerce. But that didn’t solve the problem.