Your question is Root Cause Bug Analysis. 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).
Given a scenario where a bug is reported, outline your approach to identify the root cause. Explain how you would clarify the report, reproduce the issue, narrow the investigation, collect evidence, and distinguish the root cause from symptoms. Include how you would communicate findings and validate the fix.