Coroutine stops working after first run

Premise:

I've got a button (made of a quad) working properly that references an animation curve to animate when clicked.

Issue

I can click my button once, and it'll run through the coroutine that uses the animation curve to animate it. But after that, I can't get it to trigger again. I know its still receiving the click events from the log, but the coroutine won't run after the first time its run. Any ideas why? Code for the button script below:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Button : MonoBehaviour {
 
 
     public AnimationCurve curveAnim;
     public float posDisplacement;
     public float speed;
 
     public void KickBack(){
         StartCoroutine (kickback());
     }
 
     IEnumerator kickback(){  //animation coroutine
         float curveTime = 0f;
         float curveAmount = curveAnim.Evaluate (curveTime);
 
         while (curveAmount < 1.0f) {
             curveTime += Time.deltaTime * speed;
             curveAmount = curveAnim.Evaluate (curveTime);
             transform.position = new Vector3 (transform.position.x, transform.position.y, curveAmount*posDisplacement);
             yield return null;
         }
     }
 
     //Button events called from "gameObject.SendMessage." in another script
     void OnTouchDown(){
         Debug.Log ("Touch Down!");
     }
 
     void OnTouchUp(){
         Debug.Log ("Touch Up!");
         KickBack ();
     }
 
     void OnTouchStay(){
         
     }
 
     void OnTouchExit(){
 
     }
 }