I have DX8’s. But the issue got my attention because of some weird servo responses I have been seeing lately and two giant scale crashes using them. But for your issue:<o></o>

Could your issue maybe be related to a speed setting for the Flaps and Flaps is also programmed into Aux 2? Or do you have the correct tail type selection (e.g. two servos per elevator)? However, ... Sometimes, I have had to abandon the tail types and go to normal tail and just do mixes. Sometimes, probems crop up after working well for months and I have to reset the model in the transmitter and manually program from scratch to fix the thing. Maybe you could put the two on each surface on a "Y" versus dedicating a channel to each of the 4 servos?.

Frankly, I am considering giving up on Spektrum. But, I hear some of their competitor’s horror stories also.

I recently have/had another but similar issue. I had two elevators mixed together to operate together. Occasionally on startup, the one elevator would go full up and the other would be neutral. This only happened at startup. I would have to change the mix's offset in the transmitter's mix setting to Zero (0) % to fix it. Then the next flight or two, the elevator would be full down and I would have to put the 100% offset back in. Not much of a problem now as the plane doing this crashed and was totaled. But, I am going to get this figured out on the bench or dispose of the two AR 9210s (and maybe the two DX8s) before I commit either back to a another expensive plane.