Hi everyone,
I had the same issue. What I did was following the reply of kornwaikas in this post https://www.prestashop.com/forums/topic/622554-problem-with-cart-updating-in-prestashop-172/
I replaced the theme.js file I had in my theme/assets/js folder by one I had in a fresh install.
it doesn't solve the issue but it helped me and I hope it can help other people.
Nohossat