Rigidbody speed in some senes different?!

Hello out there, the Controller of a Enemy-bullet is speeding the bullet up:

 void Update ()
     {
         rb.velocity = transform.forward * speed;
     }

In some scenes, the bullet travels at the correct speed, in others it is very very slow, but still a bit moving.

here the complete script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class EnemyBullet : MonoBehaviour {
 
     [HideInInspector]
     public float speed;
     [HideInInspector]
     public float makePlayerSlower;
     [HideInInspector]
     public float lifeTime;
     [HideInInspector]
     public ParticleSystem explosion;
 
     float lifeTimer;
     GameObject player;
     Rigidbody rb;
     bool mayDestroy = true;
     bool wasStuck;
 
     // Use this for initialization
     void Start ()
     {
         rb = GetComponent<Rigidbody>();
     }
     
     // Update is called once per frame
     void Update ()
     {
         rb.velocity = transform.forward * speed;
         wasStuck = false;
 
         lifeTimer += Time.deltaTime;
         if ((lifeTimer >= lifeTime) && mayDestroy)
             Destroy(gameObject);
     }
 
     void OnTriggerEnter(Collider other)
     {
         if(other.CompareTag("Player"))
         {
             transform.parent = other.transform;
             rb.isKinematic = true;
             player = other.gameObject;
             player.GetComponent<PlayerControl>().speedReduction = makePlayerSlower;
             player.GetComponent<PlayerControl>().AddStickyBall(gameObject);
             GetComponent<Collider>().enabled = false;
             mayDestroy = false;
             wasStuck = true;
         }
         else if(!other.CompareTag("Enemy"))
         {
             Destroy(gameObject);
         }
     }
 
     void OnDestroy()
     {
         ParticleSystem explosionClone = Instantiate(explosion, transform.position, transform.rotation);
         Destroy(explosionClone, 1f);
         if(wasStuck)
             player.GetComponent<PlayerControl>().RemoveStickyBall();
     }
 }
 

I am pretty shure, that i don't change the transform of the bullet in any other scripts! And i have now Idea...

(btw: if you have any advice for my in my way of scripting, please let me know! :D)

Thanks for reading and trying to help! WbrJr