High Logstash CPU Usage

I've been running a logstash framework for a while now that had 5 instances of logstash reading from a kafka queue, processing that data, and pushing it to elasticsearch. I discovered recently that that kafka queue only had 2 partitions, and 2 machines had taken those, and that my other 3 machines had essentially been sitting idle for quite a while. I never suspected this because, they were pretty consistently running at 70-100% all of the time EVEN THOUGH they were processing no records.

Why might this possibly be??

What versions are you running. 2.0.4 got a fix for this: https://github.com/logstash-plugins/logstash-input-kafka/issues/49