RobotLinking 18B20 pinout and circuit board weirdness
From the look of the board, it is designed to support multiple devices. I'd suspect that the three sets of holes give different mappings of the device pins to the board pins. Could it be that the sensor is soldered into the wrong set of holes?

If you have a meter or can see the traces you could look to see if the middle set of holes is wired the way you would expect. If that is a photo of your board, it looks like you have enough length in the leads on the sensor to move it to the middle holes.