Always 404 not found error when executing stackset deploy command

[kaito3desuyo]

I'm trying to deploy a CloudFormation StackSet, but I always get a 404 error on DescribeStackSetOperation.

$ rain stackset deploy example.yaml ExampleCFnStackSet --admin --config config.yaml
Stack set has been created successfuly with ID: ExampleCFnStackSet :81d4a89b-5628-40ad-b95f-9a89cac0f6c1
Submitted CREATE instances operation with ID: 62387382-145f-48fd-a0fd-984629683597
error while creating stack set instances: operation error CloudFormation: DescribeStackSetOperation, https response error StatusCode: 404, RequestID: 0dfe41ea-eae7-4003-b7bf-e2b52a6ab556, StackSetNotFoundException: StackSet ExampleCFnStackSet not found

If you look at the console, the StackSet is actually created.

When I run it again, the update tries to happen, but I get a 404 error again.

$ rain stackset deploy example.yaml ExampleCFnStackSet --admin --config config.yaml
Stack set already exists. Do you want to update it? (Y/n)
Updating stack set instances in all previously deployed accounts and regions
Submitted UPDATE stack set operation with ID: c5789d79-4535-42f1-b588-b748b65aa929
error occurred while updating stack set 'ExampleCFnStackSet' : operation error CloudFormation: DescribeStackSetOperation, https response error StatusCode: 404, RequestID: 59afd4cd-455e-465e-ab0f-b5f14f745dd8, StackSetNotFoundException: StackSet ExampleCFnStackSet not found

The configuration file is as follows.

StackSet:
  permissionmodel: SERVICE_MANAGED
  callas: DELEGATED_ADMIN
  capabilities:
    - CAPABILITY_NAMED_IAM
  autodeployment:
    enabled: true
    retainstacksonaccountremoval: false

StackSetInstances:
  deploymenttargets:
    organizationalunitids:
      - <OU ID>
  regions:
    - ap-northeast-1