Button "add to cart" have 2 actions actually: adding product to cart || refreshing the page.
When you are clicking second time at add to cart button check the "attribute size" choosen on your page
Can you provide an URL to products we can test?
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Button "add to cart" have 2 actions actually: adding product to cart || refreshing the page.
When you are clicking second time at add to cart button check the "attribute size" choosen on your page