Hi @filippettia,
From what you describe it sounds as though your theme may be overriding the default WooCommerce template files or has changed the code which outputs the Add To Cart buttons. It could also be a conflict from another plugin installed and activated on the site too.
To see if that’s the case try temporarily enabling a different theme like Twenty Twenty and look to see if the button then displays. If the buttons then display that will let you know it’s related to some code within the theme.
If not try deactivating all plugins aside from WooCommerce and see if the buttons then display. If they do enable the plugins one by one until the button disappears again and it will let you know which one is causing the conflict.
I hope this helps.
