Per the docs, it looks like the temp sensors are hooked up to a 3 position connector that supplies 3.3V. Maybe try using the 5V output from the humidity sensor connector. You may be getting too much voltage drop on the cable at 3.3V.
The VCC at the temp sensor terminal block is only about 2.7 volts, 3.3 volts via a diode, so it is too low to use. You can use the "5" volts at the humidity sensor connector (it's about 4.4 volts, 5 volts via a diode), and it will work but I have seen comments elsewhere that it is not a very clean supply. My testing is using a separate 5 volt feed to the temp sensor.