WP Debugging

In your wp-config.php, change:

define( "WP_DEBUG", false );

Into:

define( "WP_DEBUG", true );// just toggle this line to false to turn off
if ( WP_DEBUG ) {
    define( "WP_DEBUG_DISPLAY", false );
    define( "WP_DEBUG_LOG", true );
    @ini_set( "display_errors", 0 );
    define( "SCRIPT_DEBUG", true );
}

Then install a debug log viewer plugin.

When you got the debug log up and running. Add

error_log('debug log is working');

directly to your (child) theme functions.php and check if it’s working.