Soil moisture sensors that use electric resistance as a measurement of soil water potential, like gypsum block sensor or Watermark sensors, are sensitive to temperature variation.

Industry standard Watermark sensors are calibrated for 75F.
A sensor resistance of 4700 Ohm, would read as -29 kPa at that temperature (see red line in chart). The same sensor resistance at 60F would read as -25 kPa, and at 100F the reading would be -38 kPa.

In our daily practice however this is only a concern for shallow sensor installations. At installation depths of 2 feet and more, soil temperature is pretty constant and variation due to day/night temperature variation is typically not observed.