Took my P3P out for flight today, temperature was 39F.  Took off, got up to 50 feet and notice the aircraft was backing up, console then said ATTI MODE as it continued backing up.  Used controls to fly forward and hovered overhead at which point it changed back to GPS mode started behaving normally.  Uploaded flight log to airdata for analysis.  Saw yaw error started as I took off.  I flew last week, no errors.   The error at the end was me trying to grab the leg of the drone rather than having it land in snow.

You are lucky that the yaw error was small enough to still have control.
Many times a yaw error is unrecoverable.

The usual cause is launching from somewhere that the earth's normal magnetic field is distorted by the magnetic field of a steel object.
And the most common cause is launching from reinforced concrete.
Other possibilities are a bolt or screw in a wooden table or deck or a steel pipe close underground etc.

I had launched from wooden deck with screws, normally I launch from the ground but ground was covered in snow.