Hi,
Thanks for reaching out to us! I’d be happy to help you 🙂
There might be a conflict somewhere. Could you deactivate all other plugins, to see if that makes a difference? And could you switch to the default theme (Twenty Seventeen) and check again your add-to-cart function? Please read carefully our documentation about testing for conflicts before doing anything.
Furthermore, I would need your System Information in order to help you further. Could you share it with me?
Thanks in advance,
Jeremy