Session Regeneration Problem in Codeigniter – Codeigniter Session regenerate and data loss
This is usually caused by incompatibility between Codeigniter and PHP versions. For example, running Codeigniter version 3.1 on PHP 7.3.11 will result in unexpected behaviours like session regeneration.
Try upgrade to latest Codeigniter version, it should resolve the issue.
Codeigniter 3.1.11 – Session regenerate and data loss PHP 7.3.11:
https://forum.codeigniter.com/thread-75042.html