Projectile Y-axis start position issue - 2.5D Platform

I have this issue and I can't fix it. I've already tried to search on internet but I found nothing. The "projectile spawn" is situated next to my character. When I left-click on my mouse, the projectile starts shooting going forward (in the Z-axis at 20 speed, for example) but there is this issue that is making me mad. Sometimes it starts from the right place, sometimes under and under every click.

EDIT: I'm at home and this is the "shoot code". Thank you in advance.

 public Rigidbody projectile;  
 public float speed = 20;
 
 private Transform spawnPoint;
 private int SPAWN_DISTANCE = 1;
 
 void Awake()
 {
     spawnPoint = transform.Find("SpawnPoint");
 }
 
 void Update ()
 {   
      //
         if (Input.GetButtonDown("Fire1"))
         {
             atkSpeed = 0.2f;
             Shoot(projectile);
             attackTime = atkSpeed;
             chargeLevel = 0;
         }
   //
 
 }
 
 void Shoot(Rigidbody proj){
         Rigidbody _projBody = Instantiate(proj, spawnPoint.position + SPAWN_DISTANCE * transform.forward, transform.rotation) as Rigidbody;
         _projBody.velocity = transform.TransformDirection(new Vector3(0, 0,speed));
 }

HERE IS THE VIDEO: https://www.youtube.com/watch?v=GLgrfl2zU9w

EDIT2: SOLVED!