Analog Input on MKS Robin E3D / STM32F103RCT6 (no replies)

I tried to setup the analog pin 11 -> pc1 -> phys. pin 33 as input.
"Hijacked" the PC1 Pin from the Beeper with the breakout board from the bl-touch right at the exp-connector on the board.
Tested if i got the correct pin with M43 T S33 L33 R5 W1000 and voltmeter
-> fine , Pin is correct
Then i connected my sensor to the Pin (power supply for the sensor is 5V - took it from the board to have the same ground-connection)
But i get weird results from the filament width in the display.
Output from the sensor mesured is 1.98V - Display tells me 2.98.
Measured on the other side on the breakout board - 1.98V
So there should be no defect on the cable or connector.
When i set the pin to input with pullup mode the voltage goes up to 3.04V
Back at normal input 2.98 again.

The strangest thing at all is that the board tells me that there is no input at all at that pin - but displays it in the lcd ...

Send: M43 P33
Recv: PIN: 33 PC1 (A11) Analog in = 0 Input = 0
Recv: ok

The Sensor is working fine - got some help here in the forums allready

config parts in the firmware (using 2.0.5.3 bugfix)

pins.h - file for e3d:
added :
#define FILWIDTH_PIN PC1
changed :
// #define BEEPER_PIN PC1

speaker is commented out in configuration.h