.NET / dotnet script (CSX) execution in AWS CodeBuild not resolving IAM Role

We have a AWS CodeBuild Project configured with an IAM Role with the required permissions to interact with some AWS services, in this case a DynamoDB table. We are executing a dotnet-script (CSX) file which utilizes the AWS SDKs including the DynamoDB SDK to perform a PutObject operation against a DynamoDB Table.

Typically for apps and services deployed to other AWS compute services like AWS ECS/Fargate or AWS Lambda, our applications are able to just simply instantiate the SDK client(s) for the service(s) and it would follow the standard AWS credential resolution chain and we do not need to provide any explicit hint as to what credentials to be used - and ultimately the associated IAM Service Role would be resolved and utilized for all service calls (for example, var _client = new AmazonDynamoDBClient(); in a AWS Lambda Function handler, would simply utilize the configured IAM Lambda Execution Role for the use of this client).

However, that does not seem to be the case here with executing our dotnet-script/CSX file in our AWS CodeBuild Project; as we are getting a Amazon.Runtime.AmazonServiceException: Unable to find credentials (see full stack trace below with the 4 attempts/places it attempted to resolve access credentials from).

As a sanity check, we also ran a generic aws s3 ls [OurBucketName] command in the CodeBuild buildspec and its successfully listing the objects using the IAM Role configured for this same CodeBuild Project.

We tried to explicitly instantiate the DynamoDB client with the following:

var credentials = new Amazon.Runtime.InstanceProfileAWSCredentials();
_client = new AmazonDynamoDBClient(credentials, new AmazonDynamoDBConfig
{
        RegionEndpoint = RegionEndpoint.USEast1           
});
    

However, this throws:

Amazon.Runtime.AmazonServiceException: Unable to reach credentials server
   at Amazon.Runtime.InstanceProfileAWSCredentials.GetContents(Uri uri)
   at Amazon.Runtime.InstanceProfileAWSCredentials.<GetAvailableRoles>d__0.MoveNext()
   at Amazon.Runtime.InstanceProfileAWSCredentials.GetFirstRole()
   at Amazon.Runtime.InstanceProfileAWSCredentials..ctor()
   at Submission#0.DynamoDBHelper..ctor() in /tmp/codebuild/output/src767/src/s3/01/LoadStepFunctionPayloads.csx:line 39

I am able to execute the CSX file from local (with AWS credentials configured locally in the credentials files) and the script successfully resolves them.

Lastly, we have previously been able to run full .NET application/executables that leverage the AWS SDKs within CodeBuild Project and it seemed to resolve and utilize the associate IAM Service Role for the CodeBuild Project just fine.

Any guidance or pointers with working here would be appreciated!

Amazon.Runtime.AmazonServiceException: Unable to find credentials

Exception 1 of 4:
System.ArgumentException: App.config does not contain credentials information. Either add the AWSAccessKey and AWSSecretKey or AWSProfileName.
   at Amazon.Runtime.StoredProfileAWSCredentials..ctor(String profileName, String profilesLocation)
   at Amazon.Runtime.StoredProfileAWSCredentials..ctor(String profileName)
   at Amazon.Runtime.StoredProfileAWSCredentials..ctor()
   at Amazon.Runtime.EnvironmentAWSCredentials..ctor()
   at Amazon.Runtime.FallbackCredentialsFactory.<Reset>b__1()
   at Amazon.Runtime.FallbackCredentialsFactory.GetCredentials(Boolean fallbackToAnonymous)

Exception 2 of 4:
System.ArgumentException: App.config does not contain credentials information. Either add the AWSAccessKey and AWSSecretKey or AWSProfileName.
   at Amazon.Runtime.StoredProfileAWSCredentials..ctor(String profileName, String profilesLocation)
   at Amazon.Runtime.StoredProfileAWSCredentials..ctor(String profileName)
   at Amazon.Runtime.StoredProfileAWSCredentials..ctor()
   at Amazon.Runtime.FallbackCredentialsFactory.<Reset>b__2()
   at Amazon.Runtime.FallbackCredentialsFactory.GetCredentials(Boolean fallbackToAnonymous)

Exception 3 of 4:
System.InvalidOperationException: The environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY were not set with AWS credentials.
   at Amazon.Runtime.EnvironmentVariablesAWSCredentials..ctor()
   at Amazon.Runtime.FallbackCredentialsFactory.<Reset>b__3()
   at Amazon.Runtime.FallbackCredentialsFactory.GetCredentials(Boolean fallbackToAnonymous)

Exception 4 of 4:
Amazon.Runtime.AmazonServiceException: Unable to reach credentials server
   at Amazon.Runtime.InstanceProfileAWSCredentials.GetContents(Uri uri)
   at Amazon.Runtime.InstanceProfileAWSCredentials.<GetAvailableRoles>d__0.MoveNext()
   at Amazon.Runtime.InstanceProfileAWSCredentials.GetFirstRole()
   at Amazon.Runtime.InstanceProfileAWSCredentials..ctor()
   at Amazon.Runtime.FallbackCredentialsFactory.<Reset>b__4()
   at Amazon.Runtime.FallbackCredentialsFactory.GetCredentials(Boolean fallbackToAnonymous)


   at Amazon.Runtime.FallbackCredentialsFactory.GetCredentials(Boolean fallbackToAnonymous)
   at Amazon.Runtime.FallbackCredentialsFactory.GetCredentials()
   at Amazon.DynamoDBv2.AmazonDynamoDBClient..ctor(AmazonDynamoDBConfig config)
   at Submission#0.DynamoDBHelper..ctor() in /tmp/codebuild/output/src374/src/s3/01/LoadStepFunctionPayloads.csx:line 31
   at Submission#0.<<Initialize>>d__0.MoveNext() in /tmp/codebuild/output/src374/src/s3/01/LoadStepFunctionPayloads.csx:line 81
--- End of stack trace from previous location ---
   at Dotnet.Script.Core.ScriptRunner.Execute[TReturn](String dllPath, IEnumerable`1 commandLineArgs) in C:\Users\runneradmin\AppData\Local\Temp\tmpy4dcdn\Dotnet.Script.Core\ScriptRunner.cs:line 110