Kafka consumers logging "Auto offset commit failed" every few minutes -

i using kafka 0.9 "new" consumer api connect kafka 0.9.0.0. every couple of minutes, following error logged:

2016-01-27t16:38:14,584z [pool-1-thread-1] error o.a.k.c.c.i.consumercoordinator - auto offset commit failed. org.apache.kafka.clients.consumer.internals.sendfailedexception: null

here gist of broker , consumer configs.

there no corresponding/concerning log messages in broker logs, , records appear flowing through system fine. message annoyance, causing distracting alerts , noise.

i'm curious know exception means, real questions are:

1. should concerned exception?
2. if should not concerned, there way suppress tweaking consumer/broker configs?
3. if answer 2 questions above "no", rule suppressing these messages (i can logback) don't miss legitimate sendfailedexception log messages

i have same error message in different place (heron , kafkaspout)! finding following:

if use enable.auto.commit = true must not use consumer.commitasync();