Question

An IoT ingestion pipeline writes device telemetry to a Kinesis stream (8 shards), using `region_code` as the partition key. At 12:00 producers start getting `ProvisionedThroughputExceededException` (write throttling) on *some* records, but aggregate stream `IncomingBytes` is well under the 8-shard write budget (16 MB/s). The CloudWatch shard-level `WriteProvisionedThroughputExceeded` metric is high on exactly 2 of the 8 shards; the other 6 are nearly idle. Recent context: most traffic comes from two `region_code` values (`us-east`, `eu-west`) covering ~80% of devices. Triage and mitigate the write throttling despite spare aggregate capacity.