I am getting the same issue but yaw to the right..
Currently I have my RC in with DJI to assess/confirm if it's what I have observed to be phantom stick input.
My
MA will hover in place via GPS but yaw to the right all on it's own with zero physical stick input.
Have done several calibrations of the RC, varying results but ultimately after a while the issue returns.
I've also replaced the props and no change to AC behavior. Running OEM props.
The reason I concluded an RC problem was watching back the flight log in Go4, you can see yaw stick input of 20% or so to the right, but I physically was not touching the sticks to see if it would eventually stop of it's own accord, which it didn't.
It got to the point in the last flight where it would constantly pull right, and I was having to constantly yaw as equally as I could to the left in attempt to keep it "still."
DJI have first came back to me with no fault found in the RC, I sent them the log of the last flight waiting to hear back now.
While my RC has been away I've been researching/reading - potentially issues such as this could be resolved by adjusting the gain settings for pitch/roll/yaw etc.Gradually lowering the values until a positive change is hopefully observed..
This may be a different issue completely, there have been earlier version Phantom operators experiencing more lateral drift while yawing, as it the AC would slide off to one side by several feet when attempting to simply yaw on axis.