Sounds like you may have a faulty connection to the resistor, before blasting another Arduino with 24V put a 24k or 27k resistor in series with the analog input pin, that will limit current through the ESD protection diodes to less than 1 mA.
Sounds like you may have a faulty connection to the resistor, before blasting another Arduino with 24V put a 24k or 27k resistor in series with the analog input pin, that will limit current through the ESD protection diodes to less than 1 mA.