Session Var set onSessionStart is Undefined

Hello,

I am having an issue with a session variable becoming undefined. The var is set (cfparam) on the Application.cfc page in the onSessionStart function. How is it possible for the variable to be undefined if it is set when the session starts? If the session has expired, wouldn't the onSessionStart function run, thus creating the var again? I have this problem on a couple of different applications and I am not sure why it is happing. Any ideas?

CF9

Thanks,

Josh