aws-cdk: (Cloudwatch): Metrics with labels can't be used in alarms for API Gateway metrics

Just getting this with v1.92 (worked fine <=1.91) updating Cloudwatch alarm yields: Invalid metrics list (Service: AmazonCloudWatch; Status Code: 400; Error Code: ValidationError

Reproduction Steps

alarm = metric.create_alarm(
            self,
            id=id_alarm,
            alarm_description=kwargs['alarm_description'],
            threshold=kwargs['threshold'],
            period=core.Duration.minutes(kwargs['period_in_minutes']),
            comparison_operator=cw.ComparisonOperator.GREATER_THAN_OR_EQUAL_TO_THRESHOLD,
            evaluation_periods=kwargs['evaluation_periods'],
            statistic=kwargs['statistic']
        )

these are the parameters I’m passing to it:

{
        "metric_name": "5XXError",
        "label": "HTTP 5XX",
        "statistic": "sum",
        "color": "#d62728",
        "period_in_minutes": 1,
        "alarm": {
          "alarm_description": "5XX at 1 threshold",
          "threshold": 1,
          "period_in_minutes": 5,
          "evaluation_periods": 1,
          "statistic": "sum"
        }
}

What did you expect to happen?

a Cloudwatch alarm resource created/updated

What actually happened?

UPDATE_FAILED        | AWS::CloudWatch::Alarm     |  
Invalid metrics list (Service: AmazonCloudWatch; Status Code: 400; Error Code: ValidationError;

Environment

• CDK CLI Version : 1.92
• Framework Version: 1.92
• Node.js Version: 10
• OS : amazonlinux2-x86_64-standard:1.0
• Language (Version): Python (3.7)

Other

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