Thank you for your response! Unfortunately, none of those suggestions from that thread resolved my issue. I was able to fix the issue fairly simply. I may have even included an unnecessary step but here is what I did in case anyone else has this problem:
I renamed my movie folders to movies.old, movies2.old (this may have been an unnecessary step)
I then did a scan library, and my movies were removed from Plex. I then went into the library management and erased all of the folders.
Then I added the movie folders, and all of my posters were replaced!
