A DevOps Engineer is using AWS CodeDeploy across a fleet of Amazon EC2 instances in an EC2 Auto Scaling group. The associated CodeDeploy deployment group, which is integrated with EC2 Auto Scaling, is configured to perform in-place deployments with CodeDeployDefault.OneAtATime. During an ongoing new deployment, the Engineer discovers that, although the overall deployment finished successfully, two out of five instances have the previous application revision deployed. The other three instances have the newest application revision. What is likely causing this issue?

A. The two affected instances failed to fetch the new deployment.
B. A failed AfterInstalllifecycle event hook caused the CodeDeploy agent to roll back to the previous version on the affected instances.
C. The CodeDeploy agent was not installed in two affected instances.
D. EC2 Auto Scaling launched two new instances while the new deployment had not yet finished, causing the previous version to be deployed on the affected instances.