Builders like divi and Avada

Your JS link in cleanup-html.php on line 56 is relying on the wordpress function is_admin. For builders, that doesn’t come back as true because the URL isn’t wp-admin. I have changed it for my needs and it seems to work both in the backend editor and in AVADA live builder.

I removed :

// Insertion scripts
function cleanup_html_admin_scripts() {
	wp_register_script('cleanup_html_admin_scripts', plugin_url() . '/cleanup-html.js');
	wp_enqueue_script('cleanup_html_admin_scripts');
}
if (is_admin()) {
	add_action('init', 'cleanup_html_admin_scripts');
}

and added …

add_action( 'after_wp_tiny_mce', 'custom_after_wp_tiny_mce' );
function custom_after_wp_tiny_mce() {
    printf( '<script type="text/javascript" src="%s"></script>',  plugins_url('/cleanup-html.js', __FILE__) );
}

This then should load whenever the TinyMce editor is loaded.