Breaking template by adding and injecting html and postid into body tag

It sounds like the theme isn’t coded properly, the plugin code only injects IMG HTML with some styling CSS into the RSS feed output. If your theme or page template is outputting RSS from your site, then that would be affected as well.

It looks like you’re using the Renad theme, and I don’t see it using RSS for pulling in content. If you could set up a staging instance with that theme, we could troubleshoot further.