Could you please, check if the mentioned option works fine with the default WooCommerce theme? Go to Appearance > Install and activateactivtae Storefront theme > check the issue. Are you able to add product without problems when the default theme is activated?
Switch back to XStore. Do the backup of widgets and Theme Options before switching.
One standard license is valid only for 1 project. Running multiple projects on a single license is a copyright violation.