test_streaming_pipeline_returns_expected_user_metrics_fnapi_it test flaky

Looks like a streaming metrics issues. Logs: https://builds.apache.org/job/beam_PostCommit_Python36/985/testReport/junit/apache_beam.runners.dataflow.dataflow_exercise_streaming_metrics_pipeline_test/ExerciseStreamingMetricsPipelineTest/test_streaming_pipeline_returns_expected_user_metrics_fnapi_it/

 Error Message:
"Unable to match metrics for matcher name: 'ElementCount' (label_key: 'output_user_name' label_value: 'ReadFromPubSub/Read-out0'). (label_key: 'original_name' label_value: 'ReadFromPubSub/Read-out0-ElementCount'). attempted: <3> committed: <3>\nActual MetricResults:\nMetricResult(key=MetricKey(step=generate_metrics, metric=MetricName(namespace=apache_beam.runners.dataflow.dataflow_exercise_streaming_metrics_pipeline.StreamingUserMetricsDoFn, name=double_msg_counter_name), labels={}), committed=6, attempted=6)\nMetricResult(key=MetricKey(step=generate_metrics,