"Tell me about a mistake you made in production on a mobile product. What exactly happened, how did you respond in the moment, and what did you learn from it? If helpful, you can use an example from the Facebook app, Instagram, Messenger, or a similar large-scale mobile surface."
This question tests ownership under pressure. For a Mobile Engineer at Meta, shipping quickly matters, but so does protecting user experience at scale. Interviewers want to see whether you can recognize impact fast, communicate clearly during an incident, prioritize the right fix, and take responsibility without becoming defensive.
It also reveals how you behave after the immediate fire is out. Strong candidates do not stop at “I rolled it back.” They show how they diagnosed the issue, coordinated with partners, handled ambiguity when root cause was not obvious, and improved the system so the same class of failure was less likely to recur.
A strong answer is specific: name the release, the bug, the affected users, and the timeline. Structure it in STAR, focus on your own actions, quantify the impact and recovery, and end with a concrete lesson that changed how you ship mobile code today.