Water Level Sensor gives zero value at start of measurement

Great sensor, but we discovered one nasty behaviour.
When the sensor starts, and there is already a startlevel of liquid, then the sensor returns zero. Only after the the sensor was removed from the liquid and replaced again, the correct level is returned.
From a low power point of view, we would like to use the sensor in a battery powered application and thus want to automatically start and stop the sensor by a transitor-switch.
Hope you can help us.

Maybe an option is, when we can get the ATtiny1616 code. Then we can try to modify this code.