Critical error Shield session info

This happens if your first App was logged in with the same user session and which was not cleared ,  what to do is make sure that you clear or destroy the first session which was used and not destroyed

Thank you! Sessions have always been a little 'black boxy' to me. Bear with me here...
When a user closes browser or leaves the site - I need to destroy the session? I've never done that before (which is probably why I have session files that become a massive pile in the session folder over time).
I see the docs on destroying a session when logging out https://codeigniter.com/user_guide/libra...-a-session
Majority of the users will not log out on my site because they don't want to log back in - (I use Shield and have remember me active)

I'm reading more in the docs on sessions right now - so I may continue to edit this reply as I read more.

- Added after more reading
I see in Config/Session.php

** Session Expiration **
* The number of SECONDS you want the session to last. Setting to 0 (zero) means expire when the browser is closed *
public int $expiration = 7200;

So, if I set this to 0 then I remedy the CRITICAL ERROR?
But, then I need to destroy those sessions routinely as well, right? Garbage collector? (again, something I've heard of but never messed around with)
Am I on the right track? Any suggestions to add?

Thanks