Hello,
1) There is no error on that product anymore. Provide us with the link at least to one product with the error. We need to study it in more detail.
2) We can’t check the other gateways because it requires real payment information. Go to Appearance > Themes > install and activate Storefront theme and check one of the mentioned gateways. Do you have the mentioned error? Do you get the mentioned error with the XStore by yourself?
3) Provide us with FTP access to your site to check the issue with the products and banner. Provide link to page with the blog issue because you provided the wrong screenshot of the issue and I don’t understand where to check it.
Regards