shortcode not working correctly

I have multi paged post. many of them have google chart. I have used visuablizer plugin to integrate with google chart. It was working perfectly.

But, when I try to add ajax pagination it shows nothing! Just the shortcode itself.

I have applied “the_content” filter like:

function ajax_load_page(){
	$post_id = $_REQUEST['id'];
	$page = $_REQUEST['page'];

	$post = get_post($post_id);

	$content = $post->post_content;
	if ( false !== strpos( $content, '<!--nextpage-->' ) ) {
		if ( $page > 1 )
			$more = 1;
		$content = str_replace( "\n<!--nextpage-->\n", '<!--nextpage-->', $content );
		$content = str_replace( "\n<!--nextpage-->", '<!--nextpage-->', $content );
		$content = str_replace( "<!--nextpage-->\n", '<!--nextpage-->', $content );
		// Ignore nextpage at the beginning of the content.
		if ( 0 === strpos( $content, '<!--nextpage-->' ) )
			$content = substr( $content, 15 );
		$pages = explode('<!--nextpage-->', $content);
		$numpages = count($pages);
		if ( $numpages > 1 )
			$multipage = 1;
	} else {
		$pages = array( $post->post_content );
	}
	$shortcode_content = $pages[$page - 1];
	$shortcode_content = apply_filters( 'the_content', $shortcode_content);

	$previous = false;
	$next = false;

	if(count($pages) > $page)
		$next = $page + 1;
	if($page > 1)
		$previous = $page -1;

	wp_send_json(array('previous'=>$previous, 'next'=>$next, 'content'=>$shortcode_content));
}

add_action( 'wp_ajax_load_page', 'ajax_load_page' );
add_action( 'wp_ajax_nopriv_load_page', 'ajax_load_page' );

can you please what I am doing wrong?

https://wordpress.org/plugins/visualizer/