Your question is Tough Bug Discussion. 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).
Explain a tough bug you solved recently.
This was asked in the Techno-managerial, second hiring manager stage. Focus on one specific bug rather than describing your general debugging process. Explain how you isolated the cause, made trade-offs under uncertainty, collaborated with others, validated the fix, and prevented recurrence.
A strong answer uses STAR, distinguishes symptoms from root cause, describes your personal contribution, and closes with a measurable result and lesson learned.