In Hadoop metrics it's possible to register multiple metrics with the same name but with different tags. For example each RpcServere has an own metrics instance in SCM.
They are converted by PrometheusSink to a prometheus metric line with proper name and tags. For example:
The PrometheusSink uses a Map to cache all the recent values but unfortunately the key contains only the name (rpc_rpc_queue_time60s_num_ops in our example) but not the tags (port=...)
For this reason if there are multiple metrics with the same name, only the first one will be displayed.
As a result in SCM only the metrics of the first RPC server can be exported to the prometheus endpoint.