Day 2 scale in and scale out operations shows incorrect values when you have manually destroyed any of the deployments machines.
To prevent the issue, do not entitle destroy operations for deployments where Scale Out/Scale In operations are enabled. This prevents a count mismatch. If you think your deployment has a machine in a cluster that was manually destroyed, an administrator can check by counting the number of cluster members that appear on the Deployments page. If there is a cluster that has a destroyed virtual machine, redeploy the deployment and do not entitle destroy operations on the redeployed deployment.