Question Enemies do not collide when spawned with prefab spawner

(If this is the wrong forum please correct me.)
Hello! I am making a game for school which is a zombie shooter. I have the zombies spawn at an array of spawn points, it all works fine but there are occasions where some of the zombies won't take damage. The zombies have a Navmesh, Box Collider, and a Rigidbody. Here is my code concerning the spawning of the zombies:

Code (CSharp):

1. using System;
2. using System.Collections;
3. using System.Collections.Generic;
4. using Unity.VisualScripting;
5. using UnityEngine;
6. public class GameManager : MonoBehaviour
7. {
8.     public GameObject obstacle;
9.     public Transform[] spawnPoint;
10.     public int amount = 0;
11.     public GameObject Player;
12.  
13.  
14.     public void Start()
15.     {
16.         StartCoroutine("SpawnObstacles");
17.         //starts the obstacle spawning
18.     }
19.  
20.     private void Update()
21.     {
22.         amount = GameObject.FindGameObjectsWithTag("Zombie").Length;
23.     }
24.  
25.  
26.  
27.     IEnumerator SpawnObstacles()
28.     {
29.  
30.         while (true)
31.         {
32.             for (int i = 0; i < spawnPoint.Length; i++)
33.             {
34.                 if (GameObject.FindGameObjectsWithTag("Zombie").Length > 100)
35.                 {
36.                     Destroy(Player);
37.                     //Will add main menu but this is the current method of loosing
38.                 }
39.  
40.  
41.                 float waitTime = .7f;
42.                     //sets waitime
43.                     yield return new WaitForSeconds(waitTime);
44.                     //pauses before next spawn
45.                     Instantiate(obstacle, spawnPoint[i].position, Quaternion.identity);              
46.                    
47.             }
48.  
49.  
50.         }  
51.  
52.     }
53.  
54.  
55.  
56.  
57.  
58.  
59.  
60.  
61. }
62.  

If you would like my zombie class and the .asset file I can provide them.
Thanks!

 

Can someone please help?