You are deploying resources with CloudFormation StackSets across two Regions in the same account. One Region's stack operation fails and the stack instance shows the status OUTDATED. What is the likely reason for this failure?

The most likely reason for an OUTDATED status in a CloudFormation StackSet instance, especially when deploying across Regions, is a conflict with a global resource. Resources like S3 bucket names, IAM roles, or CloudFront distributions must be globally unique. If the template attempts to create a resource with a name already existing in one of the target Regions (either from a previous deployment or another account), the stack operation will fail, leading to an OUTDATED status. The other options are less likely: Changing a local template doesn't directly cause an OUTDATED status in a deployed stack instance; it would require an update operation to be initiated. If the stack hadn't been deployed, its status would likely be PENDING or non-existent, not OUTDATED. Using an outdated API version would typically result in an API error, not specifically an OUTDATED stack instance status.