Automatically load asset bundles on start from cache

Uploaded an assetBundle to a server, in my scene i have a download button that downloads the asset and caches (saves) them in the iphone documents folder, and instantiates the required object using:

 var request = assetBundle.LoadAsync("Sphere", typeof(GameObject));
 
 Instantiate(request.asset, new Vector3(0f, 0f, 0f), Quaternion.identity);

upon closing the app and reopening it i want the downloaded asset to load automatically on start, i have a script that checks if the file exists it instantiates it according to the following code

 IEnumerator Start () {
          print ("START FIRST");
         
     
          strPath = GetiPhoneDocumentsPath ();
         
          cachedAssetBundle = strPath + "/savedassetbundle.assetbundle";
         
         Debug.Log(cachedAssetBundle);
         
         if(File.Exists(cachedAssetBundle)) 
         {
             started=true;
         
         download = new WWW(cachedAssetBundle);
         yield return download;
             
             AssetBundle assetBundle = download.assetBundle;
             
 
         AssetBundleRequest request = assetBundle.LoadAsync("Sphere", typeof(GameObject));
         yield return request;
         
         Instantiate(request.asset, new Vector3(0f, 0f, 0f), Quaternion.identity);
         
         download.assetBundle.Unload(true);
         }
     }

Notes: 1) i am testing on an iPhone

2) the check for if an asset bundle exists works, as i have a game object that rotates when i close and reopen the app after downloading if started = true;

The problem is when i close and reopen the application the asset bundle doesnt load automatically on start, even though the asset bundle exists