Make a list of all integer coordinates in a sphere of a certain dimension: it works in debug but not in practice

So I'm working on a voxel game with cubic chunks. A chunk is 4m cube. I want to get a list of all the coordinates in which to spawn these chunks around the player as a sphere, to simulate a render distance. Here's my code:

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

public class ChunkManager : MonoBehaviour
{
    public List<ChunkCoordinate> chunkSlots = new List<ChunkCoordinate>();
    public ChunkCoordinate chunkSlotInsert = new ChunkCoordinate();
    public float updateCooldown;
    public int chunkSlotIndex;
    public int chunkSlotIndexX;
    public int chunkSlotIndexY;
    public int chunkSlotIndexZ;
    public bool chunkSlotUpdated;
    public int renderDistance;
    static public bool requestRDU;

    void Start(){
        requestRDU = true;
        updateCooldown = 1;
        renderDistance = 50;
    }
    void Update()
    {
        //Chunk Updator
        updateCooldown -= Time.deltaTime;
        if(updateCooldown < 0){
            updateCooldown = 1;
            if(requestRDU){UpdateRenderDistance();}
        }

        
    }
    public void UpdateRenderDistance(){
        chunkSlotUpdated = false;
        chunkSlotIndexX = 0;
        chunkSlotIndexY = 0;
        chunkSlotIndexZ = 0;
        chunkSlotIndex = 0;
        //Generate an eighth of the chunk slot sphere
        chunkSlotInsert.x = 0;
        chunkSlotInsert.y = 0;
        chunkSlotInsert.z = 0;
        chunkSlots.Add(chunkSlotInsert);
        Debug.Log(chunkSlotInsert.x.ToString() +", "+ chunkSlotInsert.y.ToString() +", "+ chunkSlotInsert.z.ToString());
        while(!chunkSlotUpdated){
            chunkSlotInsert.x += 1;
            if(Vector3.Distance(new Vector3(chunkSlotInsert.x, chunkSlotInsert.y, chunkSlotInsert.z), new Vector3(0, 0, 0)) > renderDistance){
                chunkSlotInsert.x = 0;
                chunkSlotInsert.y += 1;
                if(Vector3.Distance(new Vector3(chunkSlotInsert.x, chunkSlotInsert.y, chunkSlotInsert.z), new Vector3(0, 0, 0)) > renderDistance){
                    chunkSlotInsert.x = 0;
                    chunkSlotInsert.y = 0;
                    chunkSlotInsert.z += 1;
                    if(Vector3.Distance(new Vector3(chunkSlotInsert.x, chunkSlotInsert.y, chunkSlotInsert.z), new Vector3(0, 0, 0)) > renderDistance){
                        chunkSlotUpdated = true;
                    }
                    else{
                        chunkSlots.Add(chunkSlotInsert);
                    }
                }
                else{
                    chunkSlots.Add(chunkSlotInsert);
                }
            }
            else{
                chunkSlots.Add(chunkSlotInsert);
            }
            Debug.Log(chunkSlotInsert.x.ToString() +", "+ chunkSlotInsert.y.ToString() +", "+ chunkSlotInsert.z.ToString());
        }
        //Duplicate chunk slot info on x axis
        chunkSlotIndex = 0;
        while(chunkSlots.Count > chunkSlotIndex){
            Debug.Log(chunkSlots[chunkSlotIndex].x.ToString() +", "+ chunkSlots[chunkSlotIndex].y +", "+ chunkSlots[chunkSlotIndex].z);
            chunkSlotInsert.x = 0 - (chunkSlots[chunkSlotIndex].x + 1);
            chunkSlotInsert.y = chunkSlots[chunkSlotIndex].y;
            chunkSlotInsert.z = chunkSlots[chunkSlotIndex].z;
            if(!chunkSlots.Contains(chunkSlotInsert)){chunkSlots.Add(chunkSlotInsert);}
            chunkSlotIndex += 1;
        }
        //Duplicate chunk slot info on y axis
        chunkSlotIndex = 0;
        while(chunkSlots.Count > chunkSlotIndex){
            chunkSlotInsert.x = chunkSlots[chunkSlotIndex].x;
            chunkSlotInsert.y = 0 - chunkSlots[chunkSlotIndex].y;
            chunkSlotInsert.z = chunkSlots[chunkSlotIndex].z;
            if(!chunkSlots.Contains(chunkSlotInsert)){chunkSlots.Add(chunkSlotInsert);}
            chunkSlotIndex += 1;
        }
        //Duplicate chunk slot info on z axis
        chunkSlotIndex = 0;
        while(chunkSlots.Count > chunkSlotIndex){
            chunkSlotInsert.x = chunkSlots[chunkSlotIndex].x;
            chunkSlotInsert.y = chunkSlots[chunkSlotIndex].y;
            chunkSlotInsert.z = 0 - chunkSlots[chunkSlotIndex].z;
            if(!chunkSlots.Contains(chunkSlotInsert)){chunkSlots.Add(chunkSlotInsert);}
            chunkSlotIndex += 1;
        }
        requestRDU = false;
    }
}

[System.Serializable]
public class ChunkCoordinate{
    public int x;
    public int y;
    public int z;
}

Now as you can see, I'm debugging all of the coordinates for an eighth of the spehere, and it works just fine. However, inside the list I serialized for ease of use, it gives nothing but the last coordinate. I don't know why that happens, it's not like I didn't just debug the proper coordinate. Is it something with how Unity or C# handles List.Add()?

Either way, thanks in advance. If you need more info, I'll be glad to share. <3