None of the solutions in this thread worked for me. I think the culprit is when getting direction - using ‘get base aim rotation’ returns a direction that is constantly switching depending on your back animation (if your animation head moves a lot from side to side or if something is impeding your animation like collision). Hence your direction swaps from -179 to 179 and your character starts jittering.
The solution is to either fix your animation ( I didn’t want that) or to make a 2d blendspace with direction and speed and setting speed 0 with all direction to your idle stance. That way there is a path for the back animation to go → -179 back to idle to 179. Also the interpolation for both speed and direction MUST be 0, so the path can happen instantaneously. So frustrating, really hope Epic addresses this glaring issue. It works but without the interpolation, its less than ideal.