Thumbnails do not renew

I have been using the plugin for several months without any problems and I really enjoy it, however the last days it has been causing me a lot of frustration with an issue.

I have changed the featured images in two of my posts but the thumbnails that are shown in the contextual posts grid are the old ones. In fact, one post is shown without any thumbnail at all and the second one shows the old thumbnail. There doesn’t seem to be a way of changing that!

I have deleted the cache for the site.
I have deleted both of the old featured photos in the relevant posts.
I have entered manually the link to the new photos.

Still, nothing works. In the contextual posts grid,
Appreciate any help with that.

https://www.ads-software.com/plugins/contextual-related-posts/