The document discusses how increasing the partition count for a Kafka topic caused a "Heisenbug" by changing the hash function used to assign messages to partitions, violating the ordering guarantee within partitions. This led to Elasticsearch indexing messages out of order and failing to delete documents as expected. The bug was fixed by fully reingesting the data into a new Kafka cluster with a consistent partition count. The key lesson is not to change the partition count if an application relies on ordering of messages within a topic.