Calling `.nack()` suspends consumer group rebalance

[tkornai]

In what version(s) of Spring for Apache Kafka are you seeing this issue?

I tested the following versions, they all show the same behaviour:

2.3.13, 2.5.14, 2.6.3, 2.8.2

Describe the bug

After calling KafkaMessageListenerContainer.nack() if a consumer group rebalance is triggered then it won't finish until the nack() timeout has passed.

The extended CG rebalance prevents every member of the consumer group from progressing with message processing.

To Reproduce

Please follow the steps described in the sample repository: https://github.com/tkornai/nack-rebalance-demo

Expected behavior

Calling nack() must not delay subsequent consumer group rebalances.

Sample

A link to a GitHub repository with a minimal, reproducible, sample.