We have one mom with 3 collectors in our environment. We have upgraded CA APM from 10.5 to 10.7 SP2 but after upgrade only one collector is connecting to mom rest of two collector is not connecting.
Checking the IntrsocpeEnterpriseManager.log files on all Enterprise Managers in the cluster showed that the Build was not the same. The MOM and connecting collector both showed
Introscope Enterprise Manager Release 10.7.0.115 (Build 991408)
but the collectors failing to connect reported
Introscope Enterprise Manager Release 10.7.0.45 (Build 990045)
The Enterprise Manager versions must be consistent within a cluster
APM 10.7 SP2 had not applied correctly on problem collectors - once reapplied successfully collectors then connected.