drivers/Session_files_driver.php

Your server OS stops Apache/PHP deleting session files from /tmp folder.

I would suggest first creating folder for sessions inside your project, ideally outside public_html folder.

Then, assuming you are using Linux, you need to make OS user that runs the Apache process owner of that folder. Depending on setup, this would usually be called simply apache.

Then make sure owner (apache) has write privilege for that folder.

The actual steps vary depending on your actual OS and Apache configuration, but this should point you to right direction.