See: https://github.com/cdklabs/cdk-ecs-service-extensions/blob/main/src/service.ts#L297,305

The Application Auto Scaling API only supports a single policy against a metric at a time. By putting the value in the construct name, it is causing CloudFormation to replace the resource, which it can't do.

The error looks like this Only one TargetTrackingScaling policy for a given metric specification is allowed. (Service: AWSApplicationAutoScaling;

(This problem is present in v1 as well.)