When email logging is enabled via logging_api and an administrator modifies a user account via the manage user screen, an error message is returned:

Undefined variable: s_msg

The offending code from within the log_event() function of logging_api.php:

       case 'file':

$t_php_event = $t_now . ' ' . $t_level . ' ' . $s_msg;

error_log( $t_php_event . PHP_EOL, 3, $t_modifiers );

break;

At this point $s_msg may or may not be defined.