AWS autoscaling group automatically increases instances to balance zone capacities

I encountered one weird problem with AWS autoscaling group. My ASG availability-zones cover us-west-a/b and c. Sometimes ASG itself added EC2 instances in some zones to "aid balancing capacity across zones", making the total size of my ASG increase. What is more, when it increases instances to balance the zones, "NO LIFECYCLE HOOK WORKDE". The instances were launched immediately and no messages sent to my SQS. I'm not aware of their launching and not able to install software or terminate them. They're kind of waste.

Hope someone could answer my question Thanks! :)