How to root-cause Wi‑Fi chip stops after 30 minutes

You are running automated tests on a Wi‑Fi chip. The chip transmits normally at the beginning, but after about 30 minutes it stops transmitting (no signal observed). Assume you can modify the test, firmware, and measurement setup.

Describe a practical, step-by-step root cause investigation process. What data would you collect, what hypotheses would you prioritize, and what experiments would you run to isolate the cause?