Bot traffic that lands in only one arm
An A/B test intended a 50/50 split, but control ended up with many more users than treatment, and the SRM check fails badly. Digging in, the team finds that an automated scraper was assigned to control (its requests all fell into one bucket) and generated tens of thousands of low-value pageviews with almost no conversions. Treatment shows a +3% lift on the primary metric.
Explain how bot traffic in one arm biases the comparison, and what the team should do.
Your answer
This one is open-ended. Work it through, then check your reasoning against the full solution.