Turn on debugging without displaying it on the web pages. Errors are written to a log file in wp-content.

debug true log only wp-config.php

 // Enable WP_DEBUG mode
define('WP_DEBUG', true);

// Enable Debug logging to the /wp-content/debug.log file
define('WP_DEBUG_LOG', true);

// Disable display of errors and warnings 
define('WP_DEBUG_DISPLAY', false);
@ini_set('display_errors',0);