Same issue for me but only with Autotune PRO, all the other Autotunes (artist, EFX, etc.) are working.
if i use Autotune PRo alone, no problems at all, but if i insert another plugin before or after, a digital distorsion appears and the audio is pithed down of an octave +/-, i've tried with different plugin brands (Softube, Fabfilter, Cakewalk, and more).
Also when you insert Auto Tune Pro alone without any other plugins, the stereo wide changes and act like a doubler effect, very pleasent to be honest, but it shouldn't happen!