Not sure if this helps.

Recent* versions of CGI::Session use a recent version of Scalar::Util which includes S::U::refaddr (earlier versions don't).

I had a mismatch where it worked on my local m/c but not on my hoster (who had an early verison of S::U). Data in the session was silently corrupted and it took quite a while to track it down.

It may be worth checking the versions of these modules.

* For some definition of recent.