Collision keep resetting transform.velocity

(Sorry for my bad english)

I currently making a basic 2D player controller, and i have a weird issue. I using addForce to move, and jump, but when the character landing from a jump, and the collide happens the playertranform.velocity is resetting to 0.0, even if I held down left or right arrow, and because of this, a player stopping for a moment before start to run again.

Input code:

public bool IsJump()
{
    if (Input.GetKey(KeyCode.UpArrow)) return true;
    else return false;
}

public bool IsLeft()
{
    if (Input.GetKey(KeyCode.LeftArrow)) return true;
    else return false;
}

public bool IsRight()
{
    if (Input.GetKey(KeyCode.RightArrow)) return true;
    else return false;
}

Run state:

int direction = 0;
float speed = 60f;
float maxSpeed = 5f;
GameObject player;
Rigidbody2D playerRigid; 

public override void StateDestroy()
{
}

public override void StateStart()
{
    SetStateName("Run");       
    player = GameObject.FindGameObjectWithTag("Player");
    playerRigid = player.gameObject.GetComponent<Rigidbody2D>();
    Debug.Log("Run started");
}

public override void StateUpdate()
{
    if (stateMachine.playerInput.IsRight())
    {          
        direction = 1;
    }
    else if (stateMachine.playerInput.IsLeft())
    {         
        direction = -1;
    }        
    else 
        StopMoving();

    if (stateMachine.playerInput.IsJump())
    {
        stateMachine.ChangeState(new Jump());
    }
}

public override void StateFixedUpdate()
{       
        playerRigid.AddForce(new Vector2(direction, 0) * speed * Time.deltaTime, ForceMode2D.Impulse);
        NormalizePlayer();        
}

void StopMoving()
{
    stateMachine.ChangeState(new Idle());
}

void NormalizePlayer()
{
    if (playerRigid.velocity.x < -maxSpeed || playerRigid.velocity.x > maxSpeed)
    {
        Vector2 vec = playerRigid.velocity.normalized * maxSpeed;
        playerRigid.velocity = vec;
    }
}

Jump state:

GameObject player;
Rigidbody2D playerRigid;
float jumpForce = 300f;
float maxJump = 6f;
bool isJump = false;

public override void StateDestroy()
{
}

public override void StateFixedUpdate()
{
    if (isJump)
    {           
        playerRigid.AddForce(new Vector2(0, 1) * jumpForce * Time.deltaTime, ForceMode2D.Impulse);
        NormalizeJump();
    }
}

public override void StateStart()
{
    SetStateName("Jump");
    player = GameObject.FindGameObjectWithTag("Player");
    playerRigid = player.gameObject.GetComponent<Rigidbody2D>();
    isJump = true;
}

public override void StateUpdate()
{
    if (!stateMachine.playerInput.IsJump())
    {
        isJump = false;
    }     
}

void NormalizeJump()
{
    if (playerRigid.velocity.y > maxJump)
    {
        Vector2 vec = playerRigid.velocity.normalized * maxJump;
        playerRigid.velocity = vec;
        isJump = false;          
    }
}

Where the issue happens:

GameObject player;
Rigidbody2D playerRigid;   

private void Awake()
{
    playerInput = GetComponent<IPlayerInput>();
}

private void Start()
{
    player = GameObject.FindGameObjectWithTag("Player");
    playerRigid = player.gameObject.GetComponent<Rigidbody2D>();

    ChangeState(new Idle());
}   

private void OnCollisionEnter2D(Collision2D collision)
{
    if (collision.transform.tag != "Ground") return;

    if (currentState.GetStateName() == "Jump")
    {
        Debug.Log(playerRigid.velocity); // <-- here is the velocity is Zero. dunno why;

        if (playerInput.IsLeft() || playerInput.IsRight())
        {
            ChangeState(new Run());               
        }
        else 
            ChangeState(new Idle());
    }
}

Note: here the playerRigid is only for tracking the velocity at the collision.