Hey @Mikey, we're having a similar problem on 2 different SCA versions (2018.2 as well as 2020.2) after installing a few of the pre-built SCA extensions, particularly Gift Wrap. For us, Add-to-Cart, Add-to-Wishlist and other action buttons stopped responding to clicks on PDP, even after we removed the extension bundle from the account.
Did you get to resolve the issue on your end?