Q. I get the message: “I don’t know how to edit this post, I don’t have the form ID”
Ans: When you create a post with the new version of WP User Frontend, a form ID is being attached to that post. It’s needed because you might have 10 forms and it doesn’t know which form should be used to edit that post.
For this problem with older posts, one thing you need to do. If you go the those posts edit screen in backend, you’ll see a meta box “WPUF Form”, select the form that should be used to edit the form.