You have a Radius realm defined on the ProxySG with a Primary and Secondary server.
Health check of the Radius realm is "
OK on alt server".
The default failover is as following:
Access Request" Radius packets to both the Primary and Secondary server and the health check changes to "
OK on alt server". During this time it is the secondary server that replies with the "
Access Reject" or "
OK" and only the Primary server replies.