Session Data Lost after redirection in Codeigniter

I am using Codeigniter 3.0.6 and PHP 7.1.2. Problem that I faced is the session data lost after redirecting to another controller. After googled, this issues is kind of a bug in Codeigniter. I have tried many solution found in google and this link gives the solution that works for my case.

I did exactly the steps that are shown in that link :

1. Go to system/libraries/Session/Session.php
2. Comment session_start() by adding //. We want to relocate the sessionn_start().
3. Find (using ctrl + f ) a comment that says "Security is king". Comment out all the line under that comment until the end of the function. In my case I commented out the line number 313 - 318.
4. Go to the main index.php, it is the first index.php and located in the same directory with the sub-directories 'application', 'system', 'user_guide', etc. 
5. Put 'session_start()' right after < ?php

Hope this can help you....