set APM variable from irule LB_SELECTED

Hello.

I don't think that you are setting the APM session variable correctly which is why it is showing in the LTM logs but not in the APM logs. You can probably check this by having a look at the session variables for an existing APM session to see if this variable exists at all (regardless of the content of the variable to start with).

Please try updating the following section of your iRule

when LB_SELECTED {
ACCESS::session data set session.custom.radservermsg "[LB::server addr]"
log local0. "Radius Auth server [LB::server addr]:[LB::server port]"
}

I can't remember if the last part "[LB::server addr]" should be in quotes or not, so give it a try with and without the quotation marks if what I provided didn't work.