Coroutine endlessly looping?

Hello all. I am new with Unity and am currently making a basic character controller for a player. The problem I am having is with my jump function that I have created. I am now using an IEnumerator for the jump process, but for some reason it is re-looping itself endlessly after the first yield return. I have spent the last hour trying to find what is causing this, but there is nothing in my code that re-calls the coroutine. When I went through the code step by step, it just gets to the first return, then goes straight back in again, for some unknown reason. I have left attached my whole controller and if anybody can see what I am missing, the help would be much appreciated. Many thanks!

 public class PlayerController : MonoBehaviour {
 
     #region Variables
 
     [SerializeField]
     GameObject Cam;
 
     public float walkSpeed = 2f;
     public float runSpeed = 6f;
     public float jumpHeight = 20f;
 
     CapsuleCollider coll;
     Rigidbody rb;
     public LayerMask groundLayers;
 
     public float turnSmoothTime = 0.2f;     //seconds for smooth damp to go from current value to target value
     float turnSmoothVelocity;
 
     public float speedSmoothTime = 0.1f;
     float speedSmoothVelocity;
     float currentSpeed;
 
     bool isAttacking = false;
     bool isJumping = false;
     bool isFalling = false;
 
     float nextAttackTime = 0f;
     [SerializeField]
     float attackFreq = 0.5f;
 
     float nextJumpTime = 0f;
     [SerializeField]
     float jumpFreq = 0.5f;
 
 
     #endregion
 
 
     Animator animator;  //attach animator in editor
 
     void Start () {
         animator = GetComponent<Animator>();
         coll = GetComponent<CapsuleCollider>();
         rb = GetComponent<Rigidbody>();
     }
 
     IEnumerator Jump()
     {
         //Debug.Log("Jump called");
         animator.SetTrigger("isJumping");
         rb.velocity += jumpHeight * Vector3.up;
         yield return new WaitUntil(() => rb.velocity.y <= 10);
         isFalling = true;
         animator.SetTrigger("isFalling");
         yield return new WaitUntil(() => isGrounded());
         animator.SetTrigger("hasLanded");
         isJumping = false;
         nextJumpTime = Time.time + jumpFreq;
     }
 
     void Attack() //take in number for different attack and use if statements for playing different animations
     {
         isAttacking = true;
 
         animator.Play("Unarmed-Attack-L3");
 
         nextAttackTime = Time.time + attackFreq;
         isAttacking = false;
     }
 
     void Inputs()
     {
         if (Input.GetAxisRaw("AttackL") > 0 & !isAttacking & Time.time >= nextAttackTime)
         {
             Attack();
         }
         if (Input.GetAxisRaw("Jump") > 0 & !isJumping & Time.time >= nextJumpTime)
         {
             if (isGrounded())
             {
                 isJumping = true;
                 StartCoroutine(Jump());
             }
         }
     }
 
     void Update()
     {
 
         Vector2 input = new Vector2(Input.GetAxisRaw("Horizontal"), Input.GetAxisRaw("Vertical"));  //User input for movement
 
         Inputs();
 
         if (input != Vector2.zero)
         {
             float targetRotation = Mathf.Atan2(input.x, input.y) * Mathf.Rad2Deg;
             transform.eulerAngles = Vector3.up * Mathf.SmoothDampAngle(GameObject.FindGameObjectWithTag("MainCamera").transform.eulerAngles.y + targetRotation, targetRotation, ref turnSmoothVelocity, turnSmoothTime);    //creates a smooth turning for character
         }
 
         bool running = (Input.GetKey(KeyCode.LeftShift) | (Input.GetAxisRaw("Special") > 0));     //Shift must be held to allow running speed
         float targetSpeed = ((running) ? runSpeed : walkSpeed) * input.magnitude;     //if running, speed = run speed, otherwise speed = walk speed if magnitude = 0, speed will be 0
         currentSpeed = Mathf.SmoothDamp(currentSpeed, targetSpeed, ref speedSmoothVelocity, speedSmoothTime);   //adds smoothing between movement states
 
         transform.Translate(((Cam.transform.forward * input.normalized.y * currentSpeed) + (Cam.transform.right * input.normalized.x * currentSpeed)) *  Time.deltaTime, Space.World);   //move in direction facing, in world space
 
         float animationSpeedPercent = ((running) ? 1 : .5f) * input.magnitude;  //calculates the percent of movement speed
         animator.SetFloat("speedPercent", animationSpeedPercent, speedSmoothTime, Time.deltaTime);
         //Debug.Log("Is grounded = " + isGrounded());
         //Debug.Log("isJumping = " + isJumping);
     }
 
     bool isGrounded()
     {
         return Physics.CheckCapsule(coll.bounds.center, new Vector3(coll.bounds.center.x, coll.bounds.min.y - 0.1f, coll.bounds.center.z), coll.radius * 0.9f, groundLayers);
     }
 
 }