follow steps will reproduce this problem:
1)there is a 3 brokers kafka cluster,use kafka-console-consumer.sh to consumer one topic and suppose group named "test-consumer-group",after a while, we stop consumer this topic.
2)suppose test-consumer-group will be write offset meta to partition 3 of __consumer_offsets,and the leader of partition 3 is broker 1.
3) and we scale the cluster to 5 nodes ,and reassign partititons,and leader of partition 3 is change to 0
4)then we use kafka-consumer-groups.sh --list can't show test-consumer-group,but the offset meta still in topic __consumer_offsets
and i found that:
protocolType will be change to empty for test-consumer-group after leader changed.
filter this test-consumer-group,so we can't use kafka-consumer-groups.sh to list it