The save button from the fp-predictionform don't work when it's in a post.
In my case the post's permalink is in the p=POST_ID format.
FP rewrote it in the action attribute from the form tag with page_id=POST_ID.
So a fp-predictionform shortcode in a post isn't "available" as you can't send the form as the page didn't exist.
More globally, all the pages created by FP are in the page_id=POST_ID format.
Is it possible for it to look at the permalink setting and generate pages or link as defined ?
By the way, a workaround is to edit the file class-football-pool-pool.php and remove the content from the action attribute in line 847.
action="%s" becomes action="".
So the shortcode is fully functionnal in a post.