Add to Cart not working!

My add to cart is button is working for some products, but in some it just refreshes the page.
For example,
working in: https://smartairfilters.com/en/product/sqair-hepa-filter/
and not working in: https://smartairfilters.com/en/product/carbon-filter-for-diy-air-purifier/

(You need to select ‘Rest of the World’ in the dropdown to see the add to cart button.)

There are customizations that I have done, but these customizations are applied on all product pages. So I’m not sure why some work and some don’t.

I have disabled all customizations and still its the same.