Exchange iApp healthcheck

Basically, we are migrating from Exchange 2010 to 2013 and we are just planning to test new CAS servers under temporary test VIPs then swap the pool members of the production Exchange VIPs with the new CAS servers.

I have 2 identical health monitors generated by the same Exchange iApp for 2 different VIPs. Can someone explain to me why when putting all the ciscas? and cishyb? servers in the same pool, I get odd result from exch-oa-v2_monitorcheck_oa_http_monitor?

exch-oa-v2_monitorcheck_oa_http_monitor would show that all ciscas? are up but cishyb? servers are down while exch-2013_monitorcheck_oa_http_monitor would show that all ciscas? and cishyb? servers are up.

I have the same problem for both OA and OWA health monitors. Where should I start troubleshooting this?

ltm pool /Common/exch-2013.app/exch-2013_oa_pool {
    app-service /Common/exch-2013.app/exch-2013
    load-balancing-mode least-connections-member
    members {
        /Common/cishyb1:80 {
            address 192.168.13.200
        }
        /Common/cishyb2:80 {
            address 192.168.13.201
        }
        /Common/cishyb3:80 {
            address 192.168.13.202
        }
    }
    monitor /Common/exch-2013.app/exch-2013_monitorcheck_oa_http_monitor 
    slow-ramp-time 300
}
ltm pool /Common/exch-oa-v2.app/exch-oa-v2_oa_pool {
    app-service /Common/exch-oa-v2.app/exch-oa-v2
    load-balancing-mode least-connections-member
    members {
        /Common/ciscas1:80 {
            address 192.168.13.192
        }
        /Common/ciscas2:80 {
            address 192.168.13.193
        }
        /Common/ciscas3:80 {
            address 192.168.13.194
        }
        /Common/ciscas4:80 {
            address 192.168.13.195
        }
    }
    monitor /Common/exch-oa-v2.app/exch-oa-v2_monitorcheck_oa_http_monitor
    service-down-action reselect
    slow-ramp-time 300
}
ltm monitor http /Common/exch-2013.app/exch-2013_monitorcheck_oa_http_monitor {
    app-service /Common/exch-2013.app/exch-2013
    defaults-from /Common/http
    destination *:*
    interval 30
    password ????????
    recv "200 Success"
    send "RPC_IN_DATA /rpc/rpcproxy.dll\?oa.company.com:6001 HTTP/1.1\\r\\nUser-Agent: MSRPC\\r\\nHost: oa.company.com\\r\\n"
    time-until-up 0
    timeout 91
    username domain\\username
}
ltm monitor http /Common/exch-oa-v2.app/exch-oa-v2_monitorcheck_oa_http_monitor {
    app-service /Common/exch-oa-v2.app/exch-oa-v2
    defaults-from /Common/http
    destination *:*
    interval 30
    password ????????
    recv "200 Success"
    send "RPC_IN_DATA /rpc/rpcproxy.dll\?oa.company.com:6001 HTTP/1.1\\r\\nUser-Agent: MSRPC\\r\\nHost: oa.company.com\\r\\n"
    time-until-up 0
    timeout 91
    username domain\\username
}