Visible code appearing for Amazon images

UPDATE: This is resolved. It was NOT a GeneratePress issue - it was a Rankmath issue.

When I add an image from Amazon (using their SiteStripe), some part of the code appears next to the image. Amazon support said when they added my image links, it worked, so it must be a problem with my site rather than the image links. I have two sites on GeneratePress and it is the same problem for both. I have a third site that has a different theme and I just tried to insert an Amazon image on that site and the image looks fine (no code appearing next to it). Which makes it seem like it is the theme. Do you have any ideas on how I might troubleshoot and fix this?
Thanks,
James