Code snippet for Featured image caption causing weird issues

Hello, i am using a code snippet wich is causing weird issues in my posts. Right now i have about 60 plugins in my wordpress site. If i use the code snippet locally, everything works fine. But in production, my posts create the 502 error. Here is the code:

add_filter( 'post_thumbnail_html', 'custom_add_post_thumbnail_caption',10,5 );
 
function custom_add_post_thumbnail_caption($html, $post_id, $post_thumbnail_id, $size, $attr) {

    if ( !$html == '' && is_single() ) {
        // Get Excerpt of thumbnail
        $thumbnail_image = get_posts(array('p' => $post_thumbnail_id, 'post_type' => 'attachment'));
        $thumbnail_caption = $thumbnail_image[0]->post_excerpt;

        if ( $thumbnail_caption ) {
            $html .= '<div class="">
            <p class="">'. $thumbnail_caption .'</p>
            </div>';
        }
    }
    return $html;
}

Why can i be doing wrong? Thanks in advance.