Do you have AP Load Balancing enabled?
(BOSTON-MC-1) #show lc-cluster group-membership
Cluster Enabled, Profile Name = "BOSTON-CLUSTER-MC"
Redundancy Mode On
Active Client Rebalance Threshold = 50%
Standby Client Rebalance Threshold = 75%
Unbalance Threshold = 5%
AP Load Balancing: Enabled
Active AP Rebalance Threshold = 50%
Active AP Unbalance Threshold = 5%
Active AP Rebalance AP Count = 10
Active AP Rebalance Timer = 5 minutes
Cluster Info Table
The AP Load Balancing feature is disabled by default.