Character doesn't jump sometimes

Hello. I am using the following CharacterController and everything is working well, except that sometimes the character jumps and sometimes it doesn't when I hit the spacebar. What is wrong here?

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent(typeof(CharacterController))]
 public class RPGMovement : MonoBehaviour
 {
     public float ForwardSpeed = 8f;
     public float BackwardSpeed = 4f;
     public float StrafeSpeed = 5f;
     public float RotateSpeed = 110f;
 
     private CharacterController m_CharacterController;
     Vector3 m_LastPosition;
     Animator m_Animator;
     PhotonView m_PhotonView;
     PhotonTransformView m_TransformView;
 
     float m_AnimatorSpeed;
     Vector3 m_CurrentMovement;
     float m_CurrentTurnSpeed;
 
     private Vector3 playerVelocity;
     private bool groundedPlayer;
     private float jumpHeight = 0.9f;
     private float gravityValue = -20.81f;
 
     void Start()
     {
         m_CharacterController = gameObject.GetComponent<CharacterController>();
         m_Animator = GetComponent<Animator>();
         m_PhotonView = GetComponent<PhotonView>();
         m_TransformView = GetComponent<PhotonTransformView>();
     }
 
     void Update()
     {
         if (m_PhotonView.isMine == true)
         {
             ResetSpeedValues();
 
             UpdateRotateMovement();
 
             UpdateForwardMovement();
             UpdateBackwardMovement();
             UpdateStrafeMovement();
             UpdateJump();
 
             MoveCharacterController();
 
 
             ApplySynchronizedValues();
         }
         UpdateAnimation();
     }
 
     void UpdateAnimation()
     {
         Vector3 movementVector = transform.position - m_LastPosition;
 
         float speed = Vector3.Dot(movementVector.normalized, transform.forward);
         float direction = Vector3.Dot(movementVector.normalized, transform.right);
 
         if (Mathf.Abs(speed) < 0.2f)
         {
             speed = 0f;
         }
 
         if (speed > 0.6f)
         {
             speed = 1f;
             direction = 0f;
         }
 
         if (speed >= 0f)
         {
             if (Mathf.Abs(direction) > 0.7f)
             {
                 speed = 1f;
             }
         }
 
         m_AnimatorSpeed = Mathf.MoveTowards(m_AnimatorSpeed, speed, Time.deltaTime * 5f);
 
         m_Animator.SetFloat("Speed", m_AnimatorSpeed);
         m_Animator.SetFloat("Direction", direction);
 
         m_LastPosition = transform.position;
     }
 
     void ResetSpeedValues()
     {
         m_CurrentMovement = Vector3.zero;
         m_CurrentTurnSpeed = 0;
     }
 
     void ApplySynchronizedValues()
     {
         m_TransformView.SetSynchronizedValues(m_CurrentMovement, m_CurrentTurnSpeed);
     }
 
     void MoveCharacterController()
     {
         m_CharacterController.Move(m_CurrentMovement * Time.deltaTime);
     }
 
     void UpdateForwardMovement()
     {
         if (Input.GetKey(KeyCode.W) || Input.GetAxisRaw("Vertical") > 0.1f)
         {
             m_CurrentMovement = transform.forward * ForwardSpeed;
         }
     }
 
     void UpdateBackwardMovement()
     {
         if (Input.GetKey(KeyCode.S) || Input.GetAxisRaw("Vertical") < -0.1f)
         {
             m_CurrentMovement = -transform.forward * BackwardSpeed;
         }
     }
 
     void UpdateStrafeMovement()
     {
         if (Input.GetKey(KeyCode.Q) == true)
         {
             m_CurrentMovement = -transform.right * StrafeSpeed;
         }
 
         if (Input.GetKey(KeyCode.E) == true)
         {
             m_CurrentMovement = transform.right * StrafeSpeed;
         }
     }
 
     void UpdateRotateMovement()
     {
         if (Input.GetKey(KeyCode.A) || Input.GetAxisRaw("Horizontal") < -0.1f)
         {
             m_CurrentTurnSpeed = -RotateSpeed;
             transform.Rotate(0.0f, -RotateSpeed * Time.deltaTime, 0.0f);
         }
 
         if (Input.GetKey(KeyCode.D) || Input.GetAxisRaw("Horizontal") > 0.1f)
         {
             m_CurrentTurnSpeed = RotateSpeed;
             transform.Rotate(0.0f, RotateSpeed * Time.deltaTime, 0.0f);
         }
     }
 
     void UpdateJump()
     {
         groundedPlayer = m_CharacterController.isGrounded;
         if (groundedPlayer && playerVelocity.y < 0)
         {
             playerVelocity.y = 0f;
         }
 
         // Changes the height position of the player..
         if (Input.GetButtonDown("Jump") && groundedPlayer)
         {
             playerVelocity.y += Mathf.Sqrt(jumpHeight * -3.0f * gravityValue);
             m_Animator.SetTrigger("Jump");
         }
 
         playerVelocity.y += gravityValue * Time.deltaTime;
         m_CharacterController.Move(playerVelocity * Time.deltaTime);
     }
 }