Jump and move (CharacterController.velocity) C#

I am writing a simple code for mobile platformer the idea is that I have two touch buttons for movement forward and back and one button for jump. It works fine but the problem is that if I press movement button and then I jump the character controller jugges back before jumping. I was trying to figure out why it does that but I have run out of options.

Here is the code:

 using UnityEngine;
 using System.Collections;
 
 public class CharacterMovement : MonoBehaviour {
 
     public TouchControll moveFWD;
     public TouchControll moveBWD;
     public TouchControll jumpUP;
 
     private float speed = 5.0f;
     private float jumpSpeed = 18.0f;
     private bool canJump = true;
     private Vector3 velocity;
     private Vector3 movement;
 
     private CharacterController character;
     private Transform thisTransform;
 
     private bool jump = false;
 
     // Use this for initialization
     void Start () {
         thisTransform = transform;
         character = gameObject.GetComponent<CharacterController>();
         GameObject spawn = GameObject.Find( "Spawn" );
         if ( spawn ) thisTransform.position = spawn.transform.position;
     }
     
     // Update is called once per frame
     void Update () {
         movement = Vector3.zero;
 
         if ( moveFWD.fingerDown ) movement = Vector3.right * speed;
         else if ( moveBWD.fingerDown ) movement = Vector3.right * -speed;
 
 
 
         if(character.isGrounded){
             jump = false;
             if(!jumpUP.fingerDown) canJump = true;
 
             if(canJump && jumpUP.fingerDown) {
                 jump = true;
                 canJump = false;
             }
 
             if ( jump ) {
                 velocity = character.velocity;
                 velocity.y = jumpSpeed;    
             }
         } else {    
             velocity.y += Physics.gravity.y * Time.deltaTime;
             //movement.x *= 0.5f;
             }
 
         movement += velocity;    
         movement += Physics.gravity;
         movement *= Time.deltaTime;
         character.Move( movement );
         
         if ( character.isGrounded ) velocity = Vector3.zero;
     }
 }