Weird FindObjectWithTag and Method-Access behaviour

Hey community, i have a weird situation in my source code. The first problem is, that i can't seem to find the player with the GameObject.FindGameObjectWithTag("Player"). There is definitly a gameobject with that tag and other objects seem to find it without a problem but somehow this one doesn't.

The second one is that the 'fireRateTimer' in the 'void fire(...)' is always set to 0.5f. I can see that the fireRateTimer changes in the inspector but when i try to access it in the fire method it is always 0.5.

BulletWeapon.cs :

 using UnityEngine;
 using System.Collections;
 using System;
 
 public class BulletWeapon: IWeapon {
 
     public float basicFirerate = 0.5f; // Firerate in seconds
     public float firerate;
     public float maxFirerate = 0.1f;
     public float projectileSpeed = 10;
     public float fireRateTimer;
     public GameObject bullet;
     public GameObject player;
     private PlayerControlls playerSkript;
 
 
 
 
     // Use this for initialization
     void Start () {
         bulletType = BulletType.CLASSICBULLET;
         player = GameObject.FindGameObjectWithTag("Player");
         firerate = basicFirerate;
         fireRateTimer = firerate;
     }
     
     // Update is called once per frame
     void Update () {
         if (!isPause) {
             fireRateTimer -= Time.deltaTime;
         } 
     }
 
     public override void fire(Vector3 v) {
         if (!isPause) {
             Vector2 target = Camera.main.ScreenToWorldPoint(new Vector2(Input.mousePosition.x, Input.mousePosition.y));
             Vector2 myPos = v; // new Vector2(player.transform.position.x, player.transform.position.y);
             Vector2 direction = target - myPos;
             direction.Normalize();
             Quaternion rotation = Quaternion.Euler(0, 0, Mathf.Atan2(direction.y, direction.x) * Mathf.Rad2Deg);
             if (fireRateTimer <= 0) {
                 Debug.Log("wtf");
                 GameObject classicProjectile = (GameObject)Instantiate(bullet, myPos, rotation);
                 classicProjectile.GetComponent<Rigidbody2D>().velocity = direction * projectileSpeed;
                 fireRateTimer = firerate;
             } else if (fireRateTimer > 0) {
                 Debug.Log("firerate > 0 it is : " + fireRateTimer);
             }
 
             }
     }
 
     public override void upgrade() {
         throw new NotImplementedException();
     }
 
 }
 

and this is the class that the bulletweapon inherits from:

 using UnityEngine;
 using System.Collections;
 
 public enum BulletType {
     CLASSICBULLET, LASER
 }
 public abstract class IWeapon: MonoBehaviour {
 
     protected bool isPause;
 
     public BulletType bulletType;
 
     public abstract void fire(Vector3 v);
     public abstract void upgrade();
 
     public void pause() {
         isPause = true;
     }
 
     public void unPause() {
         isPause = false;
     }
 }