Form not popuplated

I registered it with code.
You can look it here : https://wordpress-257420-909214.cloudwaysapps.com/test/
It's a test page with only this shortcode : [mb_frontend_form id="firm-info" post_id="536"]
This id is this post : https://wordpress-257420-909214.cloudwaysapps.com/firm/asb-group-czech-republic/

All data in this post has been inputed from the metabox in wp-admin.
The form is displaying well, but no data in it...

If I put the shortcode in the post content, I see infos in custom fields, but for example if I add post_fields="title", the title is empty...

Sorry my explanation was bad...

If I put this shortcode inside the post content (it's a custom post type named firm and post ID is 536) : [mb_frontend_form id="firm-info" post_fields="title"]
Then here's what I got :

As you can see, all my custom fields like Country, Phone, ... are filled but the title is empty.

I've created a Test page with this shortcode : [mb_frontend_form id="firm-info" post_fields="title" post_id="536"]

And here's what I got :

No data at all 🙁

I just can't understand why...

And I think that by default, if post exist then it should make an update of the post. If you don't display title then it creates another post with no title and I think (it's personal 🙂 ) that it should update the current post or the ID provided in the shortcode, or at least add an option in the shortcode for example update="true" for people that just want to offer the client to update a post from the front but don't want them to create new posts...