Metrics filter does not flush aggregated metrics. it seems that Logstash::FilterWorker is not instantiated and therefore flush logic is never executed.
Could you run Logstash with the -vv option behind it and try it?
it should give some debuging output then.
i did, then i reviewed the code. the problem is that metric events are generated using the `flush` method which is never called.
PR merged - Closing.