Load gravity form via ajax using do_shortcode

I am reloading my form using ajax upon confirmation.

This is working perfectly and I am parsing my form_id to the action function fine...

// code to trigger stuff when forms have submitted
$(document).on('gform_confirmation_loaded', function(event, form_id){

    // run code for white label site editor form
    if(form_id == 12) {

        // reload our form
        $.ajax({
            cache: false,
            timeout: 30000,
            url: admin_ajax_url,
            type: 'GET',
            data: {
                action   : 'gf_reload_editor_form',
                post_id  : post_id,
                form_id  : form_id,
                isAjax   : true
            },
            success: function (data) {

                // remove the old confirmed form
                $('#gform_ajax_wrapper_'+form_id).remove();

                // reload form into our site editor aside
                $('#site_editor').prepend(data);

            }
        });

    }

});

The above code is working great.

The problem is reloading the form using do_shortcode.

class WhiteLabel
{

    public function __construct()
    {

        // ajax reload form actions
        add_action('wp_ajax_nopriv_gf_reload_editor_form', [ $this, 'gf_reload_editor_form' ], 20 );
        add_action('wp_ajax_gf_reload_editor_form', [ $this, 'gf_reload_editor_form' ], 20 );

    }

    public function gf_reload_editor_form ()
    {
        // get the form id
        $form_id = $_GET['form_id'];

        // do shortcode to output gravity form
        echo do_shortcode('[gravityform id="'.$form_id.'" title="false" description="false" ajax="true" update]');

        die();

    }
}

new WhiteLabel();

OK, so everything above looks hunky dori, that is because it is. I've tested my other custom do_shortcode functions and they output fine.

The problem lies with the do_shortcode('[gravityform ... ]')

You are probably wondering why don't I just use the gravity_form() php function...

gravity_form( $form_id, false, false, false, '', true );

This works fine too! This reloads a perfectly working ajax form.

The issue is, I need to use do_shortcode because I need to include the update property. The update property can't be used with the gravity_form() php function.

The update property is introduced using Gravity Forms: Post Update plugin which enables my form to update the current post, rather than create a new one.

So this got me thinking, when I am loading the form using the same do_shortcode method on the initial page load, I am using do_shortcode inside the loop. This is how the form must know what post data to get and pre-populate my form inputs with etc.

So I tried this..

public function gf_reload_editor_form ()
{

    // get the post id and set post data
    $post_id = $_GET['post_id'];
    $post = get_post($post_id);
    setup_postdata($post);

    // get the form id
    $form_id = $_GET['form_id'];

    // do shortcode to output gravity form
    echo do_shortcode('[gravityform id="'.$form_id.'" title="false" description="false" ajax="true" update]');

    die();

}

..thinking the the do_shortcode might think it's inside the loop. But still, this did not work either.

Any ideas please would be great thanks as I am stumped.