If an ADC input is open-circuit, the value on it is undefined; might be 0V, might be some voltage that it happens to be connected to by some high-impedance impurities on the board, might be whatever voltage it is pulled to by EMC influences. Make sure to pull the ADC line to a defined level if you ...

I designed a PCB using ESP32S3 (chip + peripheral method, not a module). The board has a PWM to DC converter circuit with a sensor connected in it. I connected its output to GPIO2 and did an ADC one-shot read in IDF. I have two PCBs with nearly identical layouts and routing of the adc collection ...