VSS is regulated 3.3v which I double checked. The analog pin feed the + input of an opamp (LMC7101) which has very high impedance. I noticed a problem when the output of the opamp was not going to zero or near zero when the input was supposed to be receiving a 0v signal. I checked the pin voltage with a VM, and sure enough, the lowest analog level is around 50mv. Doesn’t matter if it is connected to the opamp, or a pulldown, or both. Same value. I confirmed that I send a pin.write(0.0) when I need a 0v output. The pin level works properly for voltages above 50mv.