WaitForSeconds causing function to return

I am calling WaitForSeconds in a coroutine like this:

    public override IEnumerator Activate()
    {
       if (!playerAttributes.isBurned)
       {
          spriteRenderer = playerAttributes.GetComponent<SpriteRenderer>();
 
          StartCoroutine(ActiveTimer());
 
          // Mark the player as burned so burn can't be applied again while
          // this instance of burn is active;
          playerAttributes.isBurned = true;
 
          // Make character red while they are burned
          playerAttributes.GetComponent<SpriteRenderer>().color = Color.red;
 
          while (isActive)
          {
             if (!playerAttributes.isDead)
             {
                playerAttributes.currentHealth -= damage;

                Debug.Log("Activate");
                yield return new WaitForSeconds(applyInterval);
                Debug.Log("TEST");
             }
             else
             {
                isActive = false;
             }
          }
 
          // White returns the sprite to its original colors
          spriteRenderer.color = Color.white;
 
          playerAttributes.isBurned = false;
       }
 
       yield return null;
    }

this function is called like this:

    public void AttemptToInflict()
    {
       // Inflict status if RNG decides it should happen
       if (percentageChanceToInflict >= Random.Range(0, 100))
       {
          StartCoroutine(Activate());
       }
    }

This is the contents of ActiveTimer(), statusDuration is 3f:

    protected IEnumerator ActiveTimer()
    {
       isActive = true;
 
       yield return new WaitForSeconds(statusDuration);
 
       isActive = false;
    }

"Activate" prints out every time, but "TEST" never prints. applyInterval is set to 1 and is of type float. Why is the function exiting on the WaitForSeconds() call?