I am having the same problem, I have had once before.
Adding additional slides at a later date does not save the slide image. I pull it from the media file and then select upgrade, but the image is still not included.
I have not added any plugins for quite some time.
Is there a limitation to the amount of slides it can handle and if not, what could be causing this.
I really love this program, but will not rate it yet, until I can see if this is a limitation to the program.
Perhaps there is a "pro" version. (ugh)
Thanks for help from anyone.