I do not see that last image as the post cover photo. It is just the initial picture.
Are you on PeakD or hive.blog? On the former, you can edit the post, open the advanced settings, and reset the cover photo even after a post goes live, if I am not mistaken. I don't know about the native Hive interface.
I'm using hive.blog, and I can do that too. In fact, when I went to, the cover image had been reset to the first for some reason. I think it worked this time.
It looks right from here now, too.