Bug with sessions CI 4.5.1

Have you checked the documentation?
https://www.codeigniter.com/user_guide/l...sions.html

The defaults are to update every 5 minutes and automatically destroy the inactive session after 2 hours. You can use a database backend instead of files but that would not likely change the behavior. 

You can change some of the session defaults. One other option may be to use tempdata in your session.