There are several reasons a nested stack could be stuck in an UPDATE_ROLLBACK_COMPLETE_CLEANUP_IN_PROGRESS state. These are;
CloudFormation is still in the process of removing old resources, or can't remove those resources due to a dependency issue.
Resource cleanup is paused because a sibling stack of a nested stack fails to update or roll back.
For troubleshooting steps, see our detailed knowledge center article Why is my CloudFormation stack stuck in the UPDATE_ROLLBACK_COMPLETE_CLEANUP_IN_PROGRESS or UPDATE_COMPLETE_CLEANUP_IN_PROGRESS state?
For further assistance and because it would require details that are non-public information, please open a support case with AWS using the following link
Bug: Custom Resource deleted due to stack rollback is not given correct PhysicalResourceIdasked 20 days ago
Nested Stack failed to rollbackasked 10 months ago
The following resource(s) failed to create: [CitrixCloudConnectors]asked 6 months ago
My CNF stack failed with an "Internal Failure" and now I can't rollback or update it!asked 2 days ago
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Restore deleted nested stackasked 9 months ago
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Cloudformation Stack issues removing itasked 15 days ago
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Stack Create Fails: Internal Failure. Rollback requested by user.asked 4 years ago