I’m having basically the same issue. I’ve been using the Related Posts plugin for a few years. It used to pull the thumbnail from my post image, but now it just shows a random generic image – for all of my posts, even those that used to show the appropriate thumbnail. I’ve tried all 3 of your related post plugins (Related Posts, Related Posts by Zemanta, and WordPress Related posts) – all 3 have the same issue (Before you ask – I made sure only one of them was activated at a time)
You mention above a way to regenerate the thumbnails, but I don’t see that functionality on any of your plugin settings pages. Is this accomplished via one of the regenerate thumbnails plugins?
Thank you! That did the trick!
I have the WordPress Related Posts plugin deactivated right now. Before I delete it… Is there any difference between the two? Any reason why I might prefer one over the other?
Thanks for your help!