Optical Flow Sensor Testing and Setup

Hi Team, I have done optical flow calibration (Log based Calibration) for my Quad.
Quad Specifications:
FC: Mateksys H743 slim
Optical flow: Holybro PMW3901
TOW: 300gms
GPS: ublox M10Q
After Second flight calibration mentioned in testing and setup, the quad some times maintains its position, sometimes accelerate little away in pitch or roll axis. And one more error that I observed is, Pre Arm: Need Position Estimate, when I’m using optical flow as ek3_src1_velxy. If I lift the vehicle half meter from ground, then the pre arm error disappears and I can arm. I have attached the log below. Help me out!