There is no notice about CMRR of the Current channel ADC in the datasheet.
Let's set Gain as 512.
+-2.3 mV is a max diff signal (V_IIN+ - V_IIN-), isn't it?
+300...-200 mV is an absolute input voltage range.
Let voltage at the IIN+ pin is 100,1 mV,
and voltage at the IIN- pin is 100 mV.
Will the ADC return a correct result?