Hey, thanks for reaching out, I'll gladly help!
Well, try to use the 'Regenerate Thumbnails' plugin first, and see if this helps in any way.
If not, try to rearrange your related posts via the 'Edit Related Posts' button in your blog posts, which in some cases regenerates our users thumbnails.
If this doesn't help, try to set an image from one of your blogposts as featured, save you changes, and see if this helps.
If all the above mentioned propositions don't work, well, I'm afraid you are going to have to re-insert your images in your blog posts manually.
Either way, do let me know how it goes, since I'll be more than glad to help you out! Take care & have a nice day!