MirrorMaker2: no messages replicated when MM2 replicas set to 3 for IdentityReplicationPolicy

[EmiliaNowakowska]

Hello,

We have MirrorMaker2 configured on AWS EKS cluster.
We would like to have 3 MM2 replicas for active/passive replication (replication.policy.class: "io.strimzi.kafka.connect.mirror.IdentityReplicationPolicy").
Unfortunately for topics replicated with MM2 when replicas are set to 3, messages are not replicated (nothing is visible for CLI consumer).
For 1 MM2 replica or 2 MM2 replicas messages are visible in CLI consumer.

Could you please advise what are we missing in the MM2 config for 3 replicas?
Do we need some special settings for 3 MirrorMaker2 replicas?
Is it dependent on other settings? Kafka settings?

Our target cluster is Confluent Cloud cluster. Our consumer in CLI:
confluent kafka topic consume -b 2-test-mm2 -vvvv

For MirrorMaker2 config we use Confluent Cloud Global Access Key (for testing), as a final solution we would like to use Confluent Cloud API key associated with service account.
kubectl -n <namespace-name> create secret generic <secret-name> --from-literal=target-key-<API-key-name>=<API-secret-value>

apiVersion: kafka.strimzi.io/v1beta2
kind: KafkaMirrorMaker2
metadata:
name: mm2-test
namespace: kafka
labels:
Environment: test
spec:
version: 3.0.0
replicas: 3
connectCluster: "confluent"
clusters:
- alias: "source-cluster-name"
bootstrapServers: server-1:9092,server-2:9092,server-3:9092,server-4:9092,server-5:9092
config:
- alias: "confluent"
bootstrapServers: yyy-xxxxxxxxxxxxxxxxxxxxxx:9092
tls:
trustedCertificates: []
authentication:
type: plain
username: <API-key-name>
passwordSecret:
secretName: <secret-name>
password: target-key-<API-key-name>
config:
#Config storage replication
# -1 means it will use the default replication factor configured in the broker
config.storage.replication.factor: 3
offset.storage.replication.factor: 3
status.storage.replication.factor: 3
confluent.topic.replication.factor: 3
mirrors:
- sourceCluster: "source-cluster-name"
targetCluster: "confluent"
sourceConnector:
config:
replication.factor: 3
offset-syncs.topic.replication.factor: 3
sync.topic.acls.enabled: "false"
refresh.topics.interval.seconds: 60
replication.policy.separator: ""
replication.policy.class: "io.strimzi.kafka.connect.mirror.IdentityReplicationPolicy"
heartbeatConnector:
config:
heartbeats.topic.replication.factor: 3
checkpointConnector:
config:
checkpoints.topic.replication.factor: 3
sync.group.offsets.enabled: "true"
replication.policy.separator: ""
replication.policy.class: "io.strimzi.kafka.connect.mirror.IdentityReplicationPolicy"
topicsPattern: "1-test-mm2,2-test-mm2"