IMU and GPS timestamps do not match

When I using API to get the sensor data, I find that the timestamps of IMU and GPS do not match.

Details: data_imu = client.getImuData(imu_name='Imu', vehicle_name=vname) data_gps = client.getGpsData(gps_name='Gps', vehicle_name=vname)

print((data_gps.time_stamp-data_imu.time_stamp)*1e-9)

the answer is -2.667s.

Could anybody tell me the reason?