Yes, when issuing the command "show aaa authentication-server radius statistics" we see that CPPM-02 has a lot higher "ExpAuthTim". I believe the controller is using this attribute to distribute the load. Hence, this server gets a fair amount of less requests.
We have looked at the CPPM server load in vsphere, but at first glance we couldn't find any significant difference in performance.
The CPPM VM's run on different ESX hosts. We have tried to "cross-switch" the physical ESX host where the VM runs, but this didn't yield any noticeable effect in the load distribution.
RADIUS Server Statistics
------------------------
Server Acct Rq Raw Rq PAP Rq <-> ExpAuthTm Uptime
------ ------- ------ ------ <-> --------- ------
CPPM-02 28942 103379 1392 <-> 638 21:17:27
CPPM-03 551755 2980100 38753 <-> 34 15:6:42
The controller uses AOS 6.5.3.6