As I motioned in the title I'm not a noob. Do everything by the books every flight. Never seen this with my two Phantom 2's or Phantom 3 Pro until tonight. Normal take off, with 17 sats, all green, with 4 mph wind...and within about 350-450 feet my P3 starts "wondering about." Phantom just started spinning in semi-tight yawing circles with ZERO stick input. When I notice it's random movement on my iPad screen I made quick movements with the sticks (yawing) to see if the P3 was receiving my input. It was BUT it kept spinning maintaining current altitude for the most part. Immediately switched to Atti mode and regained control. Brought it in closer, flipped back to P-GPS and all was normal so I landed right away. What the devil happened? I powered down, powered up, took off and tested again....twice. No issues. • 174 P3P flights with zero issues • Latest firmware install since the day it was released • Did a cold IMU calibration last night since I hadn't done one in about 3 weeks. Did it in the same spot as before. No issues. Mod reading was at 1500 when complete. • Did a successful compass calibration right before the flight (Mod reading was at 1520-ish right before flight) • No power lines around. (I've taken off and tested from this home point site 70-80 flights at least with the P3P.) I checked the fight within the Pilot App to confirm my stick movement and more importantly my LACK of stick movement while it did it's little walk about in the air. Pict attached with notes... Any advise would be warmly welcomed.