Gun script not working in 5.6

I have just upgraded to 5.6 and a script that had been working just fine in 5.4 has just stopped working. It works for about 5 seconds when I launch the game then stops with no compiler errors.

Script for the gun:

 public GameObject bullet;
 public GameObject bulletHole;
 public float delayTime = 0.5f;
 
 private float counter = 0;
 
 void FixedUpdate ()    
  {
     if(Input.GetKey(KeyCode.Mouse0) && counter > delayTime)
     {
         Instantiate(bullet, transform.position, transform.rotation);
         GetComponent<AudioSource>().Play();
         counter = 0;
         
         RaycastHit hit;
         Ray ray = new Ray(transform.position, transform.forward);
         if(Physics.Raycast(ray, out hit, 100f))
         {
             Instantiate(bulletHole, hit.point, Quaternion.FromToRotation(Vector3.up, hit.normal));
         }
     }
     counter += Time.deltaTime;
 }

And the one for the bullet once fired from the gun:

 public float speed = 1f;

 void Start ()    
  {
     Destroy(gameObject, 5f); //Delete the bullet after 5 seconds
 }
 
 void Update ()    
  {
     transform.Translate(0, 0, speed);
 }