Ground Steering started with "U-turn"?

Plane model: Skyfun
Landing Gear: Tricycle Undercarriage
Plane Turning Diameter: 1.6m

Now I am currently trying to adjust STEER2SRV - PID for ground Steering for my plane, as I want to do Runway TakeOff.
But whenever I switch to “FBWA” or “Auto” mode for Runway TakeOff, the arduplane controller will always ask my plane to make a “U-turn” first, then only it started to run straight.
Why is this happening? Did anyone, your plane also have same situation?

Besides, after this “U-turn”, my plane always run with zig-zagging along the straight line.
Why is this happening?

I am really being troubled by these issues for a week of trying. If someone can help, that will be great. Thank you.

@HappySamuel, can you post a link to a DF log showing this problem? Also, can you tell me what the radius of turn of your vehicle on the ground is?