Using existing session data from a non-CI website in a CodeIgniter website

Another update -

I added session handler similar to this http://php.net/manual/en/class.sessionha...erface.php to create file name same as CI but it works intermittently i.e. if I try to view CI page after logging in at non_CI it logs me out but on my second attempt it preserves the session ... Hmmm??

On my further investigation I have found that CI generate session ID 40 characters long where as my non-CI site generates 32 characters long.

Is this because of different php versions? CI is on php 7 and non-CI is on php 5.6 ??