Yo, I’ve been having this issue for a while now. I have a character using a CAT rig in 3DS Max and when I import the animation into Unreal Engine 4, the stretch distorts the model, while it looks just fine in 3DS Max.
This ONLY happens if I rotate the bone.
For example, if I stretch out his palm, everything works fine in Unreal. As soon as I rotate the palm (like the images bellow), it distorts it in Unreal.
Here is a stretch test in Max:
Here is what it does in Unreal:
Here is how his Palm and Finger bones are setup in the hierarchy tab in Max:
I am not sure if this is a problem exporting from 3DS Max or Importing to Unreal.