Trim Mobile Number

Yes, VPE would help to understand where the problem lies.

Seems to be that the iRule is not fired at all. If not already, turn on debug level on apm access policy logging (System ›› Logs : Configuration : Options), and check how the session flow goes from the apm log or session report. Do you see the flow going to the iRule event?

Do you have multiple iRule events in the VPE flowchart? Normally I add an if -clause to check the event ID, to make sure that the iRule is run only in the intended iRule event in the VPE flow. Something like below. Otherwise the iRule may be triggered in the first (possibly wrong one) encountered iRule event in the flow with some unexpected results. Also make sure the iRule is attached to the apm virtual server itself.

when ACCESS_POLICY_AGENT_EVENT { 
   if {[ACCESS::policy agent_id] eq "logging"} {
     log local0.info "Username: [ACCESS::session data get session.logon.last.username]"
   }
}