When things go wrong, you can always use the super useful WordPress debug tool, WP_DEBUG.
By default, you have to paste a line of code in your wp-config.php to make the debug mode available.
By if you need to easily access the debug mode even when your site is live, you should edit your wp-config.php file and replace
if ( isset($_GET['debug']) && $_GET['debug'] == 'debug') define('WP_DEBUG', true);
Once done, simply add a GET parameter to the url of the page you’d like to debug, as shown below:
Of course, for obvious security reasons you should replace the name debug by a random word of your choice so no one will ever see your site in debug mode.