Should ConsumerCount be reported as 0 when there are no consumers connected to the broker?

The reporting criteria is not specified on Amazon MQ documentation. If there are no consumers subscribed, and if there is no datapoint present - this likely means that the reporting criteria is "Non-zero values".

• When you say that it was available 3-4 weeks before, can you confirm if the metric is still visible on CloudWatch and that it has 0 as the metric value?
• If the metric is not available on CloudWatch, it likely means that it has been inactive i.e. no datapoints were published for 14 days (or more) To retrieve datapoints older than 14 days you have to use get-metric-data or get-metric-statistics commands in the AWS CLI.

Using these steps I think you will be able to confirm if 0 is a valid metric value for ConsumerCount. Make sure to use the valid statistic (Sum, Average etc.), which is also not documented currently.

Hope this helps in answering your doubt.