I'd say something went terribly wrong. Either Pilot error or Drone error. The Typhoon H does lose GPS signal now and then, most times for very short periods that most pilots don't even notice. When it does lose the signal it is than at the mercy of the wind, but it certainly won't take off at 40 mph in one direction, or at least it shouldn't (there would have to be a major software/hardware glitch).
My comment was in regard to Ereese's video above. He said the ST16 vibrated and a warning popped up regarding GPS loss. Switching to RTH in this case is useless and would waste time. In your case, it sounds like a complete failure of one of the systems, but we won't know unless Yuneec tells you what occurred. I hope they do that so we can learn what is happening in these cases.I had 20 satellites at the time of my fly away & had only flown 5 minutes on my 3rd battery. I switched from angle to RTH but made no difference what so ever, my H was on a wild goose chase with myself jaw dropped & bemused.
The way my H flew was very erratic, swaying from side to side & flying away from me.
From realising that my H was flying on its own accord, to H crashing would be about 10 to 15 seconds.