Gravity: Tipping Bucket Rainfall Sensor - I2C & UART problem

Hi all, i have 5 units of this SEN0575 Tipping Bucket Rainfall Sensor, the sensor give the reading when raining, but after the rain stop for 1 hour, the reading should be re-zero but unfortunately the reading was fluctuated between the last reading and 0 and the reading for 1 hour and 24 hour was identical, only after i reboot the arduino, the reading return to zero (after 19.30) i am using arduino uno with i2c mode and i have two more i2c sensor (bmp30 and bh1750) in the system. When i try to use uart mode, the outcome were no different with i2c mode. In the system, the data will published to  thingspeak cloud, and i also try to read the data from serial monitor, same thing happen. All of 5 sensors show the same result, anyone own this sensor experienced this issue?