I’m looking at this page:
https://www.absorbyourhealth.com/product/oxiracetam-600mg-100-capsules-powerful-nootropic/
and the add-to-cart button works first time for me in IE11, as it did on a few other products. Clicking the button adds the product to cart.
I identified a couple of errors on the pages though I don’t think they are a cause.
1. The “Google Code for Remarketing Tag” is generating non-compliant html, contrary to the html spec:
https://dev.w3.org/html5/pf-summary/syntax.html para 10.1.6. Try disabling it.
2. The sidebar Subscribe form is submitting to an insecure location. Are you able to change the submit address to https:, or try disabling it.
If the problem still persists, try deactivating all plugins except WC and switching to the default theme to try to identify if one of those elements is causing a conflict.
Consider asking the theme vendor for support.
https://codex.www.ads-software.com/Forum_Welcome#Commercial_Products