The twist bones in exported rigs are ignored by Unity's humanoid rig, causing severe joint distortions
This is most easily seen with muscular characters. I'm using the CC3 athletic male, exported to Unity using your auto setup plugin. (The export is not the problem, as this problem also occurs with the character Reallusion offers on Unity's Asset store. It's less noticeable with that character, because his proportions are cartoonish.) Unity's human rig seems to ignore the twist bones, so any animation that would benefit from them instead becomes far worse. I'm attaching a png of CC3's athletic male. Note the wrist. (I've removed the rifle he's supporting, but that's why his hand is oriented that way.) This happens with every animation set I've tried, excepting, of course, animations that do not rotate the character's arms in ways that should use the twist bones. I've used animation sets from several animators, and tested them using characters with standard Unity rigs. (They worked fine on standard Unity characters.) I've experienced this problem in several different versions of Unity (and I have not found a version of Unity that avoids this problem). At the moment, I'm using Unity 2019.3.0f6.