Consumers not receiving messages

#### Expected behavior

Consumers, in a shared setup, should each receive messages in queue. If we have 4K messages for one topic and we have 20 consumers, each consumer should be receiving messages.

#### Actual behavior

Some of the Consumers will get the messages, while others remain ideal. With 20 consumers, only about 4 of 5 of the consumers will get messages at any given time, while the others will remain ideal.

#### Steps to reproduce

I'm not sure exactly. We're in an EKS cluster and used the Pulsar Helm deployment. By default, we have 4 pods subscribed to a single topic in Pulsar. Once messages are published to that topic, the messages route to those 4 pods. HPA rules in Kubernetes will then spin up more pods, each of which subscribe to the same topic.

#### System configuration
**Pulsar version**: 2.7.1

I've included the stats and internal stats read out from Pulsar. Let me know if you need anything more.

[stats.txt](https://github.com/apache/pulsar/files/6380202/stats.txt)
[stats-internal.txt](https://github.com/apache/pulsar/files/6380203/stats-internal.txt)

Start by examining the attached stats.txt and stats-internal.txt files alongside the shared-topic setup described for Pulsar 2.7.1, Kubernetes, and EKS. The issue names no source file or test entry point; done means identifying why consumers remain idle after HPA adds pods and verifying that messages are distributed across the consumer group.

Written by the indexing model from the issue text.