I’m having the same issue. I tried this solution, but I’m not seeing results. Using the shortcode with the “default=” statement. This feed – https://rssfeeds.freep.com/freep/news generally (not today) sends many posts without images. I pulled their feed, and they’re sending a blank.gif. I tried to overwrite that with that code, but it didn’t work.
Let me know what you would need to see to troubleshoot.
Thanks!