Grenade spawns in the wrong location

In my game I want to have a floating monster that's attack throws a grenade at the player. My problem is that the grenade only spawns in 0, 0, 0. In my script I make it so that the zombies spawns in on its own location but for some reason that doesn't work. I tried making it spawn by having the spawn location equal new Vector3(100, 100, 100) but it still spawned at 0, 0, 0. I know that the co-routine runs because I put a Debug.Log. Thanks for the help!

Edit #2: I can't have a rigidbody on the script. I have edited the movement script and I have found that no mater what if a rigidbody is added then it will go to 0, 0, 0.

Edit #3: I updated the scripts

Here is my script: (Sorry if the code is bad)

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ZKAttack_lvl3 : MonoBehaviour
{
    public Transform Player;
    public float MoveSpeed = 2.0f;
    public float InRadius = 10.0f;
    public float AttackRange = 15.0f;

    private Coroutine hasCourutineRunYet;

    public GameObject grenade;
    public GameObject FloatingMonster;
    private Vector3 FloatingMon;
    private Animator anim;
    private Rigidbody rigid;

    private void Start()
    {
        anim = GetComponent<Animator>();
        Player = GameObject.FindGameObjectsWithTag("Player")[0].transform;
        rigid = GetComponent<Rigidbody>();
        
    }

    void Update()
    {
        Player = GameObject.FindGameObjectsWithTag("Player")[0].transform;
        transform.LookAt(Player);

        float dstSqr = (Player.position - transform.position).sqrMagnitude;
        bool inRadius = (dstSqr <= InRadius * InRadius);
        bool inAttackRange = (dstSqr <= AttackRange * AttackRange);        
        anim.SetBool("AttackingPlayer", inAttackRange);
        if (inRadius)
        {
            transform.position += transform.forward * MoveSpeed * Time.deltaTime;
        }

        rigid.AddForce(1, 10, 1);

        if (inAttackRange)
        {
            if (hasCourutineRunYet == null)
            {
                hasCourutineRunYet = StartCoroutine(GrenadeAttack());
            }
        }

        
    }

    IEnumerator GrenadeAttack()
    {        
        FloatingMon = FloatingMonster.transform.position;        
        GameObject bulletObject = Instantiate(grenade, FloatingMonster.transform.position, Quaternion.identity);       

        yield return new WaitForSeconds(2.0f);
    }
}

Edit: This is the code for the movement:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class GrenadeMovement : MonoBehaviour
{
    public float speed = 10f;

    public float lifeDuration = 4.0f;

    private float lifeTimer;

    private Coroutine hasCourutineRunYet;
    
    private Transform Player;

    public SphereCollider sphereCollider;
    

    // Use this for initialization
    void Start()
    {
        lifeTimer = lifeDuration;

        sphereCollider.enabled = false;     

        Player = GameObject.FindGameObjectsWithTag("Player")[0].transform;
    }

    // Update is called once per frame
    void Update()
    {   
        lifeTimer -= Time.deltaTime;

        if (lifeTimer >= 3f)
        {
            Player = GameObject.FindGameObjectsWithTag("Player")[0].transform;
            transform.LookAt(Player);

            transform.position += transform.forward * speed * Time.deltaTime;
        }

        if (lifeTimer >= 0f)
        {
            transform.position = speed * transform.up * Time.deltaTime;         
            transform.position = speed * transform.forward * Time.deltaTime;            
        }


        if (lifeTimer <= 0f)
        {
            if (hasCourutineRunYet == null)
            {
                hasCourutineRunYet = StartCoroutine(GrenadeExplosion());
            }

        }
    }

    private void OnTriggerEnter(Collider coll)
    {
        if (coll.gameObject.tag == "Player")
        {
            if (hasCourutineRunYet == null)
            {
                hasCourutineRunYet = StartCoroutine(GrenadeExplosion());
            }
        }


    }

    IEnumerator GrenadeExplosion()
    {
        sphereCollider.enabled = true;

        yield return new WaitForSeconds(1.0f);
        Destroy(gameObject);
    }
}