Featured image and post image swapped

For some reason, the featured image and images from my posts have been swapped, and when I go into look at certain posts the featured image and the post images will be from different posts on my blog. For example, this article:

https://www.nerdophiles.com/2014/09/06/outlander-rent-recap/

which shows the featured image of this article:

https://www.nerdophiles.com/2012/12/22/my-love-affair-with-fringe/

The same goes with many other articles on the site. I think it might have occurred when I switched the site over from .com to .org but this problem still occurs on articles written afterwards as well. Can someone help me out?