Hi,
You are running in to BugId 420284. What happens is iRules run in tmm and Access Policy (login page, etc) run in apd. When APD get the session variable from tmm it will cache the results and it will not update the cached results even if the variable has change in tmm, the BugId is to change this behavior. Please open a case with F5 Support asking your company to be linked to the BugId.
Now... you do have some options to workaround this limitation. If you can share exactly what you are trying to do with a screenshot of the VPE, show all information that would be needed to troubleshoot and provide your iRule I can help come up with a way to make this work for you.
Seth