Zilla KafkaGroup stream stuck on decoding FindCoordinatorResponse

[bmaidics]

Describe the bug
When performance testing QoS2 publish, after a while Zilla get's stuck on allowing MQTT clients to connect. We start the group stream from MQTT-Kafka, the KafkaClientGroupFactory sends the FindCoordinatorRequest, Kafka replies with the FindCoordinatorResponse, but we never decode that packet.

To Reproduce
Steps to reproduce the behavior:

1. Run Zilla locally with basic mqtt-kafka broker config
2. Run emqtt bench pub until the the benchmark hangs (you might need to stop and run multiple times):
   ./emqtt_bench pub -h localhost -p 1883 -q 2 -c 100 -I 10 -t bench/%i
3. After that not even a simple connection is accepted by Zilla. Try:
   mosquitto_pub --url mqtt://localhost:1883/qos2 -V 5 -q 2 --message "QOS 2" -d -i "client-id"
4. The client hangs until timeout

To further debug, put a breakpoint on these codes:
KafkaClientGroupFactory.ClusterClient#doEncodeFindCoordinatorRequest
KafkaClientGroupFactory#decodeFindCoordinatorResponse

Notice that decodeFindCoordinatorResponse is never called.
I've ran local Kafka (bitnami/kafka:3.5), after a zilla restart the issue is resolved.