Why can't I see any new Kafka data after shutting down the instance and restarting it?

A community member created a cron job which published to a Kafka topic at fixed intervals. The instance was shut down and then restarted. The community member noticed that, even though the Kafka ingestion tasks were running, no new data was appearing in the datasource. The solution was to reset the Kafka offset. Here’s a bit more explanation and context.