Mix Animations with Locomotion system

I have the locomotion set up using animation clips that only animate the legs. When I try to play an upperbody animation using AddMixingTransform it completely stops the locomotion system when the animation plays. How do I mix upper body and lower body animation clips and keep the locomotion system running?

This is the code I am using (which has no effect):

 Start(){
     animation["wavearms"].AddMixingTransform(mixTransform);
 }
 
   
 Update(){
        if(Input.GetButtonDown("TEST")){
            animation.Play("wavearms");
                 
             }
 }

I've tried many different things for the mixTransform variable as well, such as making it recursive (to animate all children) and use different bones. Nothing has worked.