Consumer Lag Keeps Growing Even After Adding More Consumers

A clickstream topic has 8 partitions and is consumed by a group enrichment-service currently running 8 consumer instances (one partition each). Traffic has grown, and consumer lag (the gap between the latest offset in each partition and the offset each consumer has processed) is steadily increasing across all 8 partitions. An engineer proposes scaling the consumer group from 8 to 16 instances to "add more processing power."

1. Explain why this specific scaling move will not reduce lag, and what it will actually accomplish.
2. Diagnose at least two other plausible root causes of the lag growth and how you'd distinguish between them.
3. Describe the actual fix(es) available, including any tradeoffs.