Kafka leader crash data loss

Customer support escalates: ~40 minutes of order events appear to be missing from the downstream warehouse, but only for one product line. The producing service writes to a Kafka topic (acks=1, min.insync.replicas not set, RF=3). Dashboards show: a broker (the leader for 6 of 24 partitions) crashed and was replaced 45 minutes ago; UnderReplicatedPartitions spiked then recovered; consumer lag is zero; producer error rate stayed flat the whole time; the missing orders all hash to partitions whose leader was the crashed broker. No producer retries fired. How do you confirm the loss, mitigate now, and recover the lost orders?