Ajax form resubmission after failed validation (causes invalid error message)

Hi,

I was just testing a form and found an issue when ajax is enabled. I have tested this on several forms and can reproduce the error.

So if you create a basic form e.g. post_title

add_filter( 'rwmb_meta_boxes', 'dc_product_register_meta_boxes' );

function dc_product_register_meta_boxes( $meta_boxes ) {
    
    $meta_boxes[] = [
        'title'   => 'Products',
        'post_types' => 'product',
        'storage_type' => 'custom_table', 
        'table'        => $wpdb->prefix . 'dc_products',
        'id'      => 'dc-product',
        'context' => 'normal',
        'fields'  => [
            [
                'type'  => 'text',
                'name'  => 'Title',
                'id'    => 'post_title', 
                'class' => 'dc-post-title',
                'limit' => 50, 
                'required' => true,
            ]
        ],
    ];

    return $meta_boxes;
}

Then add the shortcode to a page with ajax enabled
[mb_frontend_form id="dc-product" confirmation="Your post has been successful" ajax="true"]

Go to the form and enter the post title field as 'test'. The form fails and displays the error message

add_filter( 'rwmb_frontend_validate', function( $validate, $config ) {
    
    if ( 'dc-product' !== $config['id'] ) {
        return $validate;
    }
    if ( $_POST['post_title'] == 'test' ) {
        $validate = 'test error'; // Return a test error message
    }
    return $validate;
    
}, 10, 2 );

Then go an update the post title to be anything else (so it validates) and then you will see that instead of the form submitting successfully you see the following error message
"Invalid request. Please try again."

I have tested this several times and cannot get it to validate if the form fails using 'rwmb_frontend_validate'. I assume the problem is from
/mb-frontend-submission/src/Shortcode.php (line 104)

Thanks