Random objects in a loop after a specific time and without back-to-back-repeats

So I want to spawn random objects ( the goodies), but without one of them spawning back to back. This is the best solution I´ve come up with but now unity freezes when I start the game (also happened with Thread.Sleep). Does anyone have an idea?

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 
 public class Instantiate_House : MonoBehaviour
 {
 
     
     public Transform Spawnpoint;
     public GameObject house; 
    
     public float spawnTime;
     public float spawnDelay;
 
 
      public GameObject[] pieces;
      public int pieceSpawn;
     private int i;
     void Start()
     {
       
   InvokeRepeating("Spawn_House",spawnTime,spawnDelay);
     }
 
     
     void Update()
     {
   
     }
 
    public void Spawn_House(){
 
         pieces = new GameObject[8];
          pieces[0]=GameObject.Find("GoodieA");
          pieces[1]=GameObject.Find("GoodieB");
          pieces[2]=GameObject.Find("GoodieC");
          pieces[3]=GameObject.Find("GoodieD");
          pieces[4]=GameObject.Find("GoodieE");
          pieces[5]=GameObject.Find("GoodieF");
          pieces[6]=GameObject.Find("GoodieG");
          pieces[7]=GameObject.Find("GoodieH");
 
  
 int i= 8;
 
 pieceSpawn = UnityEngine.Random.Range (0,7);
 
       switch (pieceSpawn)
             {
                 case 0:
                 pieceSpawn = UnityEngine.Random.Range (1,7);
                 break;
                 case 1:
                 while (pieceSpawn==1)
                 {
                     if (pieceSpawn==i)
                     {
                         pieceSpawn = UnityEngine.Random.Range (1,7);
                     }
                 }
                 break;
                 case 2:
                                 while (pieceSpawn==2)
                 {
                     if (pieceSpawn==i)
                     {
                         pieceSpawn = UnityEngine.Random.Range (0,7);
                     }
                 }
                 break;
                 case 3:
                                 while (pieceSpawn==3)
                 {
                     if (pieceSpawn==i)
                     {
                         pieceSpawn = UnityEngine.Random.Range (1,7);
                     }
                 }
                 break;
                 case 4:
                                                 while (pieceSpawn==4)
                 {
                     if (pieceSpawn==i)
                     {
                         pieceSpawn = UnityEngine.Random.Range (0,7);
                     }
                 }
                 break;
                 case 5:
                                                 while (pieceSpawn==5)
                 {
                     if (pieceSpawn==i)
                     {
                         pieceSpawn = UnityEngine.Random.Range (0,7);
                     }
                 }
                 break;
                 case 6:
                                                 while (pieceSpawn==6)
                 {
                     if (pieceSpawn==i)
                     {
                         pieceSpawn = UnityEngine.Random.Range (0,7);
                     }
                 }
                 break;
                 case 7:
                 pieceSpawn = UnityEngine.Random.Range (0,6);
                 break;
                 default:
                  pieceSpawn = UnityEngine.Random.Range (0,7);
                  break;
             }
 
              i=pieceSpawn;
                 GameObject newObject = Instantiate(pieces[pieceSpawn],  Spawnpoint.position + new Vector3 (Random.Range (-50,50),0,Random.Range (-50,50)), Spawnpoint.rotation* Quaternion.Euler (90f, 0f, 0f));
         Destroy (newObject,7);
 
         
 
     }
 
 }