"Tell me about a mistake you made in production on a mobile product. What happened, how did you realize it, how did you fix it, and what did you learn from it? If helpful, use a concrete example from a surface like Facebook, Instagram, Messenger, or WhatsApp."
This question tests ownership under pressure. For a Mobile Engineer at Meta, interviewers want to see whether you can respond calmly when a production issue affects real users, make good trade-offs quickly, communicate clearly across functions, and improve the system so the same class of failure is less likely to happen again.
It also reveals whether you are honest about mistakes. Strong candidates do not minimize the impact, hide behind team language, or focus only on the technical fix. They explain the user impact, the decision they made, how they coordinated with others, and how they changed their own process afterward.
A strong answer is specific: name the feature, release path, severity, timeline, and user impact. Structure it in STAR, spend most of the time on your actions, quantify the result, and end with a concrete lesson plus a preventive change you personally drove.