How can I solve this layering problem in Unity 2D?

Question

I have a function that creates, in an isometric perspective, a ground made out of n*n blocks, n being the length of one side, just like in the example below. All the creating is made from scratch, by that I mean that, my scene was almost all empty.

The thing is that when I introduce a length of 1 digit(from 1 to 9) the script works well. But when I try adding another digit to that one, making the length > 9, it makes the last block look like that. I assume that it is layered 1 layer behind and I don't understand why.

That problem is only when I try changing my length while the game is running. When I change to a length>9 before running, it works well. I think it is a layering problem but I don't know. I am a beginner after all. :)

In any case here is my script:

using System.Collections;
using System.Collections.Generic;
using System.Linq.Expressions;
using UnityEngine;

public class CreateField : MonoBehaviour
{
    [SerializeField] Camera _cam;
    [SerializeField] GameObject _sprite;
    [SerializeField] GameObject _groundContainer;
    [SerializeField] int lungime;
    int lastLungime;

    float _height, _width;

    private void Start()
    {
        if(lungime<1) lungime = 1;
        lastLungime = lungime;
        _width = lungime;
        setCameraResolution();
        createField(new Vector3(0, _height, 0));
    }

    void setCameraResolution()
    {
        _height = _width / _cam.aspect;
        _cam.orthographicSize = _height;
    }

    void deleteField()
    {
        for(int i = 0; i < _groundContainer.transform.childCount; i++)
        {
            Destroy(_groundContainer.transform.GetChild(i).gameObject);
        }
    }

    void createField(Vector3 offset)
    {
        for(int i=1; i<= lungime; i++)
        {
            for (int j = 1; j <= lungime; j++)
            {
                Vector3 pos = new Vector3((i-j), -(i + j) / 2f, 0) + offset;
                GameObject newSprite = Instantiate(_sprite, pos, _sprite.transform.rotation);
                newSprite.transform.parent = _groundContainer.transform;
                newSprite.name = "ground("+i+","+j+")";
            }
        }
    }
    private void Update()
    {
        if (lastLungime != lungime)
        {
            deleteField();
            _width = lungime;
            setCameraResolution();
            createField(new Vector3(0, _height, 0));
            lastLungime = lungime;
        }
    }
}

With that said, the problem is most likely in the Update(), but I don't see it.

Some more pictures for reference:

Answer 1

I tried different things but it did not work. That's when I taught to use the position.z. I multiplied length*length and then I summed it with the pos.z of the camera, then, for every block, I did this:

newSprite.transform.position += new Vector3(0, 0, diff--);

This way, the first block placed will be of cam.pos.z-lungime*lungime, and then we decrease till the last block placed will be cam.pos.z.