Recently, we visited the sensor and did some in-field fixes to the thermistor. The temperature now seems to be sending back sensible readings now and we can see the day night cycle in the stream temperature pretty well. Our conductivity sensor, on the other hand, is behaving pretty strangely.
It also shows a daily cycle in readings, closely aligned to our temperature readings. Our conductivity sensor is simply two aluminium plates (1.5 cm x 1.5 cm) held about 1.5 cm from each other. The units on our conductivity sensor currently has no real meaning. The values from the voltage divider are simply scaled between 0 and 1 for the time being.
We are also noticing that our sensor seems to wake up twice within 5 minutes every day around midnight or 1:00 am. Our sensor doesn't keep track of time on the device, so this is a pretty weird fault and it appears to be affecting our battery voltage and conductivity. The sensor should never really wake up twice like that, so it leads us to believe that the device has trouble connecting around that time and does it twice.