Random velocity changes

I have a character that moves with rigidbody. When i jump, i looks find, but sometimes, my character boost up while in the air and get out of the map very fast. I checked, and when it happens, it says the velocity is at about 210 or around it. i just happen when i walk and i jump. It happen like 5% of the time. why is it happening and how can i fix it ?`using System.Collections; using System.Collections.Generic; using UnityEngine;

 public class playerManager : MonoBehaviour
 {
 float xMovement;
 float zMovement;
 float xPosition;
 float yPosition;
 float zPosition;
 public float runningSpeed;
 public Animator animator;
 public Camera camera;
 public float cameraHeight;
 public float cameraAngle;
 public bool isOnGround;
 public float jumpForce;
 Rigidbody playerRigidbody;
 public float gravityMultiplier;
 Vector3 vel;
 public float airSpeed;
 public float groundSpeed;
 public bool canJump = true;
 
 void Start()
 {
     playerRigidbody = GetComponent<Rigidbody>();
     vel = playerRigidbody.velocity;
 }
 
 void Update()
 {
     
     xPosition = transform.position.x;
     yPosition = transform.position.y;
     zPosition = transform.position.z;
     PlayerMovements();        
     CameraManager();
 }
 
 
 public void CameraManager()
 {
     camera.transform.position = new Vector3(xPosition+cameraAngle,cameraHeight,zPosition+cameraAngle);
 }
 
 
 public void PlayerMovements()
 {
     //Jump
     if(Input.GetKeyDown(KeyCode.Space) & isOnGround == true & canJump == true)
     {
         runningSpeed = airSpeed;
         canJump = false;
         playerRigidbody.velocity = new Vector3(xMovement,0,zMovement);
         playerRigidbody.angularVelocity = Vector3.zero;
         playerRigidbody.constraints &= ~RigidbodyConstraints.FreezePositionY;
         playerRigidbody.AddForce(transform.up * jumpForce);
         playerRigidbody.drag = 0;

     }
     
     
     //Move the Character
     if(isOnGround == true)
     {
         xMovement = Input.GetAxis ("Horizontal");
         zMovement = Input.GetAxis ("Vertical");
         Vector3 distanceToMove = new Vector3(xMovement,0,zMovement);
         playerRigidbody.AddForce(distanceToMove * runningSpeed);
     }
 
     
     //Make the player face the direction he's going at
     transform.LookAt(new Vector3(xPosition+xMovement,yPosition,zPosition+zMovement));
     
     
     
     //Trigger Idle or Running Animations
     if(xMovement != 0 | zMovement != 0)
     {
         animator.SetBool("Run", true);
         animator.SetBool("Idle", false);
     }
     if((xMovement < 0.05f & xMovement > -0.05f) & (zMovement < 0.05f & zMovement > -0.05f))
     {
         animator.SetBool("Run", false);
         animator.SetBool("Idle", true);
     }            
 }
 
 
 public void OnCollisionEnter(Collision collidedOBJ)
 {
     if(collidedOBJ.gameObject.tag=="Finish")
     {
         Debug.Log(playerRigidbody.velocity);
         Debug.Log(runningSpeed);
     }
     if(collidedOBJ.gameObject.name == "Ground")
     {
         playerRigidbody.drag = 49;
         playerRigidbody.constraints &= RigidbodyConstraints.FreezePositionY|RigidbodyConstraints.FreezeRotationX|RigidbodyConstraints.FreezeRotationY|RigidbodyConstraints.FreezeRotationZ;
         isOnGround = true;
         canJump = true;
         runningSpeed = groundSpeed;
     
         
     }
 }
 
 
 public void OnCollisionExit(Collision exitCollidedOBJ)
 {
     if(exitCollidedOBJ.gameObject.name == "Ground")
     {
         isOnGround = false;
         
     }
 }
 
 
 

}

`