I have about 20 flights on the quad with no issues and had done the compass calibration twice.  Then today in Atti. mode it randomly started banking hard and wouldn't respond.  Luckily I switched into Manual mode just in time to save it.  Next test flights had same problem and so it's still controllable but seemed weird and it would sometimes become super-sluggish on the controls, and always normal in Manual mode.  I then did the compass calibration again and now it seems fixed.  So what happened?  I didn't make any changes to the quad.  While adjusting the gps mount offset angle a few times, I did forget to recalibrate after the last very slight change, but that seems an unlikely cause because I did about 10 flights after that with no issue.  

To clarify, do you use GPS mode as well? Are you flying in minimal wind?Is the unit up to date with the latest firmware? Have you done an IMU calibration?

Hi, I do use GPS mode, but wasn't when the problem occurred.  I did try switching into GPS mode and it was erratic as well - wouldn't hold position.  It was very minimal wind yesterday.  In Assistant Software, it says no f/w update available.  For IMU I did the check and it said not needed.

I guess nobody has any further ideas.  It's a bad first impression as I thought DJI would be rock solid, yet it did something even my junk naze32 on my racing quad has never done. (Which I also have gps on, I might add).