Recent Post Thumbnails don't show

Hi,

Using the featured image has worked in the past, but any new posts made recently don’t display the thumbnail. The older posts still work, just not new ones.

I am using the Streamline_30 theme. I tried switching to another theme and the problem doesn’t exist, so clearly the problem is with the theme, but I’m not sure how to fix it. I don’t understand how it can only be a problem with recent new posts.

website is: jamespaulcorreia.com

Any help would be greatly appreciated.