Mobile client version skew
At 15:00 you deploy backend v77, which changes a JSON API response: the field 'is_premium' (boolean) is replaced with 'subscription_tier' (string). Web clients update instantly and are fine. But over the next 6 hours, crash reports from the iOS app climb steadily, all on a null-pointer reading 'is_premium', and they're disproportionately from older app versions. App Store review for the new client build is still pending. Triage and mitigate.
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 40 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.