One of the three consumers has become unresponsive. What will happen to the partitions? What will happen if it becomes responsive again?

If one of the three consumers hangs, the behavior with partitions depends on the system and settings:

• In Kafka, for example, a partition can be assigned to only one active consumer in a group. If a consumer hangs, the partitions it was processing will not be processed until a rebalance occurs.
• Usually, the system detects that a consumer is unresponsive (via heartbeat timeout) and initiates a rebalance — partitions are redistributed among the remaining active consumers.

If a hung consumer "unhangs" and starts responding again:

• It will rejoin the group and may receive back the partitions during the next rebalance.
• In some systems, conflicts or duplicate processing may occur if idempotency is not configured.

Thus, a consumer hang results in temporary inaccessibility of its partitions, and recovery involves rejoining and load redistribution.