By default, max.in.flight.requests.per.connection == 5, means Kafka will send up to 5 messages to broker in parallel. How can it manage the order if those message go into the same partition in parallel?
Kafka cannot guarantee ordering of those messages if you set retries > 0.
If you want to have ordering guarantees you need to set this value to max.in.flight.requests.per.connection == 1.
The explanation is given in the Kafka doc on producer configs retries:
Allowing retries without setting max.in.flight.requests.per.connection to 1 will potentially change the ordering of records because if two batches are sent to a single partition, and the first fails and is retried but the second succeeds, then the records in the second batch may appear first.