WooCommerce Grouped Products – "Sorry, this item is not available"

Hey folks!

Stumbled into a funny one… Could it be the latest update?

I’ve created a grouped product – actually duplicated a previous grouped product and attached some subproducts.

Unfortunately, it is impossible to add any of the products to cart; you’re simply told “Sorry, this product is unavailable.”

The stocks are all set, everything else seems to be right.

You can add the products individually on their own page, but you can’t add a group from this parent page.

Any ideas?