yes that are measurement mistakes. and you know when you bring water to the soil, it takes time.
The volume (WET or SoilWatch10) is different, but the results should be more or less the same.
A soil is also never homogenous. I used the sand because this kind of soil constructions are used for football and golf.
At the moment the sensor is connected with a wireless Lorawan node since Sunday (Dragino mini dev). Every 5 minute I receive a measurement, see the attachment as an example.