Yaw Drift with new F550 Hexacopter

We assembled a new F550 yesterday, took it out in very cold weather for initial flight testing, and observed a significant constant yaw. I checked the dataflash, and it seems the yaw and desired yaw are consistent. I would much appreciate if anyone can identify the flaw.
2019-01-22 12-48-22.bin (685.0 KB)

Maybe something was wrong with radio calibration: Yaw trim is at 1411


Set it manually at 1500 in the parameter list and try another flight.


Thanks. That is the second time I discovered an unintended YAW Trim on a flight controller. It must have been there from a previous user. I probably should reset all parameters before recycling a flight controller.