This is what's confusing, I'm just wondering if maybe it wasn't auto-landing. It just lost altitude due to a bad reading from the internal barometer. The drone thinks it's hovering at 8 ft, then it maybe thinks the altitude went up to 11 ft, so it corrects itself by lowering altitude (when in all reality, it was actually at 8ft all the time) in which case this correct causes itself to start lowering making it look like it's auto-landing.
I think the logs will tell you more, but it's a mystery that does need solving! I can tell you this though, my stock drones, even with an upgraded gps, they won't hold a pinpoint position by any means. They'll drift back and forth, up and down, it's just natural. My first green cube.. I can put that drone on the floor with no props on and watch the altimeter vary by a couple of hundred feet in a matter of minutes. So no matter what, there's always the probability of faulty hardware causing some erratic drone flying.
