adding items, price amount does not change

Hello,
If I try to add items of the same product subtotal does not change.
https://dev.caseificioilbattistero.it/shop/parmigiano-reggiano/elisir-di-parmigiano/
Only when adding in the cart it show the right price.
It happens only with variable products, without add-ons.

I already contacted Woocommerce support which says that that price comes from the theme.
https://wordpress.org/support/topic/adding-items-price-amount-does-not-change/

Please any help on this?
thanks a lot!

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