Unable to select size variation

We have WooCommerce installed with our Divi theme. We have never had this issue before, but noticed it recently when a customer called and told us that they could not select a different size shirt that we sell.

Our products by default have “medium” as the default size variation. But the user should be able to select a different size from the dropdown. However, recently when users click the dropdown, only “medium” shows. It does not show the other sizes. The only way a user can get it to show the other sizes is if they click “clear” next to the sizes and color choice dropdowns.

We have several colors and size variations for each shirt. It shows the shirt color choices because we have “no default color” set. But because we have a default size set, they are unable to change the size.

We are currently having to go through all of our products and set them to have “no default size”. This is not the kind of solution that we want to be having though.