Hi wadnet srl,
I am really sorry for the delay of this reply as it is a weekend for us here.
I guess you publish that blog post from backend right?
If yes, that will be the issues, because if you publish post from backend, thus the URL generated did not go through sh404SEF, you need to publish your post in frontend, if not the blog URL won't be correct and hitting 404 error, the reason for this is because sh404SEF plugin does not run in backend and the URLs are not proccessed.
Can you try publish a new blog post from frontend, it should show correct link.