The Tarot 810 is an awesome frame, but their smaller ones definitely miss the mark.
I have been following this thread and it looks like you have tried everything. I agree to try another
controller and see what happens. I can't believe the frame is that far off to cause these problems
although I have been known to be wrong before. I just believe the problem lies with the controller
or your radio. You don't suppose you have a messed up stick in the radio? Calibration should
have shown this.
If you have one, prolly the easiest to set up and trouble shoot with is a Vector.
I bought the Arris 680 hexacopter and ordered some longer carbon arms to make it a 810 hexacopter. Right now I"m in the process of setting the gains on my naza v2 and that seems to be the only problem that I have at the time and even without the gains fine tuned it still flies great. I was waiting on some new motor adapters to replace the one I broke or I would have it finished by now.
Have you considered that you might have a bearing sticking on a motor causing the problem. I had 2 that froze up on me while in a hover and I was able to sit it down before it crashed. Worth thinking about