Codeigniter 3.1.11 - Session regenerate and data loss PHP 7.3.11

I guess I will answer this myself then.

I got this partially working by applying a solution from another thread where the REGEX was incorrect when checking the cookie. However this only partially works or works sometimes. This logic is not always executed so I think there is another place in the standard CI session code which also needs to be changed.

\system\libraries\session\Session.php

//Line 136 changed by me on 12.15.2019 -mb
//OR ! preg_match('#\A'.$this->_sid_regexp.'\z#', $_COOKIE[$this->_config['cookie_name']])
OR ! preg_match('/^[0-9a-f]/', $_COOKIE[$this->_config['cookie_name']])