I integrate the EC SENSOR on my board but I have a square wave of 2.5khz after CD4060BN

Hello I use the schematic above to put this circuit on my board

But I face the following problem, the voltage level it’s constante until the mid range of sensor, example
measuring 475 us/cm I face 600mv
1ms/cm → 200mv
but 1.8 ms/cm → 400 mv
(My real values are not theses it’s just to see the ideia)
I not sure why this is happing but i see that my waveform after CD4060B is a squarewave of 2.5khz is this correct I not sure but I read somewhere that using this circuit I receive a 20khz .
Can someone confirm that to me and help me with my problem ?
The wierd is that always close to the mid range of the sensor, the behavior change
I used all kinds of range