High-speed I/O bugs involve silicon (MAC/PHY), board (SI, routing), and software (driver, firmware). Collect PHY margin, MAC counters, and protocol trace in one review.
A package or board-path change requires reviewing which prior SI evidence and assumptions still apply.
Temperature affects PHY margin — test at corners.
Protocol trace and PHY margin are complementary but still need clocks, resets, configuration, counters and traffic context.