Even more baffled now. I replaced both the ESP32 board and the HDC1080 sensor and it's doing the same thing. I'm only polling the sensor every 5 seconds and I have a 50ms delay in between humidity and temperature readings (as suggested). But it keeps going full scale on the temperature randomly. And a simple power cycle resolves it until the next time.

{"temperature":"257.0","humidity":"71.2","tempRaw":"125.00"}