Hi there,
I wonder if this is related to our theme or not. Would you please kindly change the theme to default WordPress theme and deactivate the Cornerstone plugin to make sure all of our code is out of the way and then test the case?
If it is still not working you will need to contact the developer of the plugin to follow up.
If it is working then turn the theme back to the X but do not activate Cornerstone. Again test the case.
The only customization we have done for Woocommerce can be found in wp-content/themes/x/woocommerce folder of the theme.
We did not make any fundamental changes and used the standard guideline Woocoomerce suggest.
Thank you.