Can Vss left floating?
You need to either ground Vss or bias it negatively at any time, Vss cannot be
floating. The potentiometer can still be written with new values but EEMEM
cannot be programmed when Vss is floating. According to the designer of the
part, the AD5232 has two grounds; DGND and Vss. DGND acts as a reference point
for the digital pads only. The rest of the digital logic, including the EEPROM
along with the RDACS are powered between Vdd and Vss.