Reading a session variable in CI3 that was set by CI4

Yes, I'm aware of that. I thought I had made all necessary changes.

If I

Code:

log_message('debug',log_message('debug', 'session ci4: ' .$_SESSION['destination']));

In CI4 the session is set.

When I read all sessions from CI3, after the page has redirected, the session I set is not there. 

I thought changing the savePath and cookieName in CI4 to match CI3 would take care of that change.  My syntax for setting / getting the session vars does seem to be correct in CI3 and CI4.  It's just that CI3 isn't seeing the session in CI4.  

    public string $savePath = 'ci_sessions_CI3';