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If you have an oscilloscope, could you check the voltage levels on SCL and SDA when trying to program or read from/write to the temperature sensor? If the tag board is powered over USB, VDDIO will be 1.8v (if I remember the schematic right), so ensure that the I2C sensor's min operating voltage is 1.8v or below. And I think VDDIO will be VBAT (which should be 3V) when running with a battery. So see if running with battery power makes a difference.