On Windows server, PHP 7.0.8 , XAMPP and get this error intermittently. Have been using an older version of XAMPP, CI and PHP 5 for 2 years and never encountered this issue. After upgrading to PHP 7.0.8, CI 3.0.6 this occurs. Opcache is disabled as well.
(When traffic or load is more this occurs, not sure I might be wrong)