Loading different bundles give me a null exception

Hello, to summarize my problem, I've a loading menu scene and couple of missions..each package of mission has an 3 asset bundles assigned for them (Textures/prefabs and objects/scene). at the start of the game, I've a checker function that directs me to the corresponding asset bundles to be downloaded. What works is loading each mission individually. Like either bundle 1 or 2 or 3 or 4. but when I try to navigate through, load other bundles if one is already loaded...the bundles download and load but when I instantiate an object it gives me a null exception error..

         case 1:
             if (SceneSwitch) {    
                         string q1mats = "https://robogarden.s3.amazonaws.com/Visualizer/AssetBundles/J1/Q1/j1q1mats";
                         www = WWW.LoadFromCacheOrDownload (q1mats, 17);
                         yield return www;
                         www.assetBundle.LoadAllAssetsAsync ();                    
                         //Bar.fillAmount += 0.2f;
 
                         string q1prefabs = "https://robogarden.s3.amazonaws.com/Visualizer/AssetBundles/J1/Q1/j1q1prefabs";
                         wwwww = WWW.LoadFromCacheOrDownload (q1prefabs, 16);
                         yield return wwwww;
                         wwwww.assetBundle.LoadAllAssetsAsync ();
                         //Bar.fillAmount += 0.3f;
                         string sceneURL1 = "https://robogarden.s3.amazonaws.com/Visualizer/AssetBundles/J1/Q1/j1scene";
                         wwww = WWW.LoadFromCacheOrDownload (sceneURL1, 21);
                         yield return wwww;    
                         //Bar.fillAmount += wwww.progress / 3f;
                         wwww.assetBundle.LoadAllAssetsAsync ();
                         SceneSwitch = false;
                         SceneLoad = SceneManager.LoadSceneAsync ("game");
                         //Bar.fillAmount += SceneLoad.progress;
                         yield return SceneLoad;            
                     
 
             }
             RenderSettings.skybox = mat;
             break;
 
         case 2:
             if (SceneSwitch) {
                         string q2mats = "https://robogarden.s3.amazonaws.com/Visualizer/AssetBundles/J1/Q2/j1q2mats";
                         www2 = WWW.LoadFromCacheOrDownload (q2mats, 17);
                         yield return www2;
                         www2.assetBundle.LoadAllAssetsAsync ();
                         //Bar.fillAmount += 0.2f;
 
                         string q2prefabs = "https://robogarden.s3.amazonaws.com/Visualizer/AssetBundles/J1/Q2/j1q2prefabs";
                         wwwww2 = WWW.LoadFromCacheOrDownload (q2prefabs, 16);
                         yield return wwwww2;
                         wwwww2.assetBundle.LoadAllAssetsAsync ();
 
                         //Bar.fillAmount += 0.3f;
                         string sceneURL1 = "https://robogarden.s3.amazonaws.com/Visualizer/AssetBundles/J1/Q2/j1q2scene";
                         wwww2 = WWW.LoadFromCacheOrDownload (sceneURL1, 21);
                         yield return wwww2;    
                         //Bar.fillAmount += wwww.progress / 3f;
                         wwww2.assetBundle.LoadAllAssetsAsync ();
                         SceneSwitch = false;
                         SceneLoad = SceneManager.LoadSceneAsync ("game");
                         //Bar.fillAmount += SceneLoad.progress;
                         yield return SceneLoad;                    
                     
                  
             }
             RenderSettings.skybox = mat;
             break;

Thanks in advance !