Unity - Jump counter for double jump script not working? C#

It was working fine last night but it doesn't work today, the zJumpCount stays at zero after I jump now. If the zJumpcount stays at zero my double jump code doesn't work. I even ctrl+z'd back to the beginning of the session with no luck.

public class zPlayerMovement : MonoBehaviour {

  public float zMoveSpeed;
  public float zJumpThrust;          
  public bool IsGrounded; 
  public float zJumpCount;
  private Rigidbody zRB;    

  void Start () {
    zRB = GetComponent<Rigidbody>();
  }

  void Update () {

    if (IsGrounded == true) 
      zJumpCount = 0f;

    if (Input.GetKey(KeyCode.A))
      zRB.transform.Translate(Vector3.left * zMoveSpeed);

    if (Input.GetKey(KeyCode.D))
      zRB.transform.Translate(Vector3.right * zMoveSpeed);

    if(Input.GetButtonDown("Jump") && IsGrounded == true)
    {
      zRB.AddForce(Vector3.up * zJumpThrust, ForceMode.VelocityChange);
      zJumpCount++;
    }

    if (IsGrounded == false && zJumpCount > 0 && zJumpCount < 2)
    {
      if (Input.GetButtonDown("Jump"))
      {
        zRB.AddForce(Vector3.up * zJumpThrust, ForceMode.VelocityChange);
        zJumpCount++;
      }
      if (IsGrounded == false && zJumpCount >= 2)
      {
        if (Input.GetButtonDown("Jump"))
          return;
      }
    }
  }

  void OnCollisionStay (Collision collisionInfo)
  {
    IsGrounded = true;
  }

  void OnCollisionExit (Collision collisionInfo)
  {
    IsGrounded = false;
  }
}