Can't add score in Unity

I'm trying to add +1000 to a score when my player hit an item (I'm trying to do an endless runner game).
I have in my game manager the following code:

    private float currentScore = 0;
    void Update(){
        if(!isGameEnded){
            currentScore = Time.timeSinceLevelLoad * 10f;
            if(scoreBonus){
                currentScore += 1000;
                scoreText.SetText(currentScore.ToString("0"));
                scoreBonus = false;
            }
            scoreText.SetText(currentScore.ToString("0"));
        }
    }

And I have an itemCollision script in which I update my GameManager's scoreBonus variable:

    void OnCollisionEnter(Collision collisionInfo){
        if(collisionInfo.collider.tag == "Player"){
            FindObjectOfType<PlayerCollision>().ActivateInvicibility(invisibilityDuration);
            FindObjectOfType<GameManager>().scoreBonus = true;
            Destroy(gameObject);
        }
    }

The thing is when I hit the item, the score update really fast, I can see the +1000 happened and then it disappear. I've tried to log the score but everything seems normal, when he hits an items, its value changes in the log but not in my score text.

This issue is this line here

currentScore = Time.timeSinceLevelLoad * 10f;

This overrides any change you make to current score, since the score is the result of a calculation.

To keep things easy, you can make another variable to store additional score points, then add the two together when displaying.

private float currentScore;
private float bonusScore;

..

if (scoreBonus)
{
    bonusScore += 1000;
}

scoreText.SetText((currentScore + bonusScore).ToString("0"));