Your question is Diagnosing a Client Performance Escalation. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Walk me through a time you diagnosed a complex application performance issue for a client. What methodology did you use to isolate the problem, and how did you present your findings and recommendations back to the client?