Your question is Isolating an Intermittent Production Bug. 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).
Tell me about a time you ran into an intermittent, hard-to-reproduce bug in a product or test environment. How did you narrow down the possible causes, work with others to isolate it, and ultimately get it resolved?