bq34z100-g1 big drop of remaining capacity

Dear all,

I use several bq34z100-g1 chips now and I find one of them acting abnormally. 

When discharging, the remaining capacity keeps dropping. However, the remaining capacity stop dropping as it reaches around 20%. When it becomes 0%, I see the big drop from 20% to 0%

The battery is calibrated before and loaded with the correct Chem ID and calibration data.

S L61