Prefab not rendering when declaring Transform variable

When making enemy AI, i ran into an issue that made my enemy’s not render right.
(my game is still in prototype phase)

This is the code i am using

public class enemy_behavior : MonoBehaviour
    public float speed;
    public Transform playerTransform;
    Rigidbody2D rigidBody;

    void Start()
        playerTransform = GameObject.FindGameObjectWithTag("Player").transform;
        rigidBody = GetComponent<Rigidbody2D>();

    void FixedUpdate()
        Vector3 direction = playerTransform.position - transform.position;
        transform.rotation = Quaternion.LookRotation(direction);
        rigidBody.AddForce(transform.forward * speed);

So for more detail.
The thing that it makes it stop rendering properly is this line of code in script

playerTransform = GameObject.FindGameObjectWithTag("Player").transform;

I spawn them with this line of code

                   GameObject Spawnedenemy = Instantiate(enemy, new Vector3(transform.position.x + Random.Range(10, 50), transform.position.y - Random.Range(10, 50), 0), Quaternion.identity) as GameObject;

And this is what it schould look like: