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LTC4151 - Current Measurement Discrepancy


We are using LTC4151HMS#TRPBF and LTC4151IMS-1#PBF with a 0.02 ohm shunt and the reading we are getting on current does not match the load current.

See below current discrepancy between measured and reported from I2C. The voltage values are accurate. 

These values are for U2 schematic below.

Load: 198 mA, Measured LTC4151: 251 mA

Load: 214 mA, Measured LTC4151: 266 mA

Load: 255 mA, Measured LTC4151: 322 mA

Load: 178 mA, Measured LTC4151: 223 mA

Load: 167 mA, Measured LTC4151: 211 mA

Load: 162 mA, Measured LTC4151: 208 mA

We are using the code and examples shown in the datasheet and can measure the value on the I2C line.

See below snips from the schematic:

From the layout - the ground is stable for both (ISO_GND and GND).

Any suggestions?