Question about deleting expired session files.

I'm using latest stable version 3.x of CI with file system as session driver & sess_regenerate_destroy as false, and need help to understand why aren't old sessions files deleted.

As from CI documentation, I understood that the Garbage Collector should delete the expired session file automatically.

I can see that there are more than 800 session data files exist in folder specified by sess_save_path since last 2 months while my site has only 10 users and I was expecting files only to be a few and rest should be deleted automatically by Garbage Collector with time.

Can anyone help me to understand why are those files there and if I need to delete them by some script then what it should be?