Session issue

downgraded from 
php 7.2
ci 3.1.9

to

php 5.6
ci 3.1.0

login success

data stored in session using `$this->session->set_userdata(array())`

data dump shows data in session object `$this->session->userdata()`

redirects to home page

session has nothing in it

tried both files and db options


any help in this regard will be appreciated