GPS Guided Modes not Working ARDUCOPTER 3.5.5 OCTAQUAD Pix2.1 Here GPS

HI All

I am having trouble with GPS guided modes (Pos Hold, Loiter, RTL)

POShold:

When entering POShold from lateral movement, the copter brings itself to a stop. But after a second or so it begins to drift with the wind. (the telemetry still reports POSHOLD). when I give a slight stick input the copter “re-enters” poshold and stops the drift, but as soon as I center the sticks the drift starts again. the drift can be in any direction, as per the external disturbance. I can push the copter by hand 10m off its desired position without any resistance.

Loiter:

When i enter loiter mode, same thing the copter drifts but I have zero control though the pitch and roll inputs.

RTL:

Upon commanding RLT, the copter raises to the desired RLT alt, but then just starts to drift with the wind. No positive motion towards home point.

Regards