The ADC in the fuel gauge is 12 bits (see the datasheet block diagram) while the Current register 16 bits, so only the 12 most significant bits of the current register are measured. The least significant 4 bits represent zero-average noise, so it is normal for these bits to jump around from measurement to measurement. The LSB size if the actual ADC measurement is 25uV/Rsense (2.5mV for a 10mΩ Rsense), so any fluctuations smaller than this value can be ignored. To verify the accuracy of current measurement, check that the AvgCurrent register matches the expected value after applying a DC current for one minute (the default time constant of the averaging filter is 5.625s).