Problem when deploying a SageMaker Multi-Model Endpoints with AWS CDK/CloudFormation

I am trying to automate the deployment of a SageMaker multi-model endpoints with AWS CDK using Python language (I guess it would be the same by directly writing a CloudFormation template in json/yaml format), but when trying to deploy it, error occurs at the creation of the SageMaker model.

Here is part of the CloudFormation template made with the cdk synth command:

Resources:
  smmodelexecutionrole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Statement:
          - Action: sts:AssumeRole
            Effect: Allow
            Principal:
              Service: sagemaker.amazonaws.com
        Version: "2012-10-17"
      Policies:
        - PolicyDocument:
            Statement:
              - Action: s3:GetObject
                Effect: Allow
                Resource:
                  Fn::Join:
                    - ""
                    - - "arn:"
                      - Ref: AWS::Partition
                      - :s3:::<bucket_name>/deploy_multi_model_artifact/*
            Version: "2012-10-17"
          PolicyName: policy_s3
        - PolicyDocument:
            Statement:
              - Action: ecr:*
                Effect: Allow
                Resource:
                  Fn::Join:
                    - ""
                    - - "arn:"
                      - Ref: AWS::Partition
                      - ":ecr:"
                      - Ref: AWS::Region
                      - ":"
                      - Ref: AWS::AccountId
                      - :repository/<my_ecr_repository>
            Version: "2012-10-17"
          PolicyName: policy_ecr
    Metadata:
      aws:cdk:path: <omitted>
  smmodel:
    Type: AWS::SageMaker::Model
    Properties:
      ExecutionRoleArn:
        Fn::GetAtt:
          - smmodelexecutionrole
          - Arn
      Containers:
        - Image: xxxxxxxxxxxx.dkr.ecr.<my_aws_region>.amazonaws.com/<my_ecr_repository>/multi-model:latest
          Mode: MultiModel
          ModelDataUrl: s3://<bucket_name>/deploy_multi_model_artifact/
      ModelName: MyModel
    Metadata:
      aws:cdk:path: <omitted>

When running cdk deploy on the Terminal, the following error occur:

3/6 | 7:56:58 PM | CREATE_FAILED | AWS::SageMaker::Model | sm_model (smmodel)
Could not access model data at s3://<bucket_name>/deploy_multi_model_artifact/. 
Please ensure that the role "arn:aws:iam::xxxxxxxxxxxx:role/<my_role>" exists 
and that its trust relationship policy allows the action "sts:AssumeRole" for the service principal "sagemaker.amazonaws.com". 
Also ensure that the role has "s3:GetObject" permissions and that the object is located in <my_aws_region>.
(Service: AmazonSageMaker; Status Code: 400; Error Code: ValidationException; Request ID: xxxxx)

What I have:

• An ECR repository containing the docker image
• A S3 bucket containing the model artifacts (.tar.gz files) inside the "folder" "deploy_multi_model_artifact"

To test if it is a IAM role issue, I tried to replace MultiModel by SingleModel and replace s3://<bucket_name>/deploy_multi_model_artifact/ with s3://<bucket_name>/deploy_multi_model_artifact/one_of_my_artifacts.tar.gz, and I could create successfully the model. I am then guessing that it is not a problem related with the IAM contrary to what the error message tells me (but I may make a mistake!) as it seems .

So I am wondering where the problem comes from. This is even more confusing as I have already deployed this multi-model endpoints using boto3 without problem.

Any help would be greatly appreciated !!

(About Multi-Model Endpoints deployment: https://github.com/awslabs/amazon-sagemaker-examples/blob/master/advanced_functionality/multi_model_xgboost_home_value/xgboost_multi_model_endpoint_home_value.ipynb)