I am not sure that a server is marked out of service when load balancing is configured.
If you enable notification logging on authmgr, you should see the out of service messages.
First configure logging on the MM at the proper context:
config t
logging security process authmgr level informational
wr mem
Then after a few seconds, go to the MD and confirm that logging has been enabled for authmgr:
(aruba7640) # show logging level verbose
LOGGING LEVELS
--------------
Facility Level Sub Category Process
-------- ----- ------------ -------
arm warnings N/A N/A
network warnings N/A N/A
security warnings N/A N/A
security informational N/A authmgr
security warnings ids N/A
security warnings ids-ap N/A
system warnings N/A N/A
user warnings N/A N/A
wireless warnings N/A N/A
Then on the MD, do a "aaa user delete" to remove all users to trigger authentication
Next, look for "Taking and Bringing" messages in Authmgr to see your server bring brought in and out of service:
(aruba7005) #show log security all | include Taking,Bringing
Apr 15 09:30:29 authmgr[20731]: <124015> <20731> <NOTI> |authmgr| Bringing Server ClearPass-DUD back in service.
Apr 15 09:31:27 authmgr[20731]: <124014> <20731> <NOTI> |authmgr| Taking Server ClearPass-DUD out of service for 10 mins
Apr 15 09:52:09 authmgr[20731]: <124015> <20731> <NOTI> |authmgr| Bringing Server ClearPass-DUD back in service.
Apr 15 09:53:01 authmgr[20731]: <124014> <20731> <NOTI> |authmgr| Taking Server ClearPass-DUD out of service for 10 mins
You can also do a "show aaa load-balance statistics server-group <server group>" to see the requests in each server group to see what is being used.