title: Kafka consumer in group skips the partitions
body: <p>I've a single consumer which consumes a topic. Topic has 6 partitions. Single consumer assigned to the group. 
  I do poll like below 
  <code>Consumer.poll(10000)</code>
  I exit the consumer fetch when no records return.</p>
  
  <p>From the documentation I believe poll return empty when no records to consume and duration 10000 is enough to rebalance and fetch records.
  Most of the times poll consumes records from all partions but some times poll fetched record from 3 partitions and return empty records with out consuming other 3 partitons.</p>
  
  <p>BTW, I used 2.0.1 Kafka client and Kafka server version is 2.11 - 2.2.0.</p>
  
  <p>Any one have idea why my consumer skipping other partitions and return empty records.what should I do to consume all partitions.</p>