I keep seeing a random thumbnails showing up in the feed. Below is an example. The blog post has multiple photos (link), yet the feed shows something from my footer instead of the main blog post. Here is the feed I’m using which shows everything else working fine (link).
When the RSS feed does not have any thumbnail, then it tries to fetch the first image in the post content. In your case, the first image is not recognized by the parser for somereason.
This logic might need an enhancement. I’ll handle this in the next version.