Your team runs a production Dataflow streaming pipeline reading from Pub/Sub and writing to BigQuery. Over the past week, an on-call engineer notices that the end-to-end latency has crept from seconds to over 30 minutes, even though input message rate is roughly constant and the job has not been redeployed. Autoscaling is enabled with a generous maximum worker count, but the job is holding steady at only 3 workers. Which action should you take first to diagnose the root cause of the growing latency?