Async parse.com query not working on Android/iOS

When I try to make an asynchronous Parse.com request to fetch data, the task does not seem to get completed. This works within the Unity Editor, but not when running on an Android or iOS device.

I had this working until a few days ago, I re-architected my code a bit and been having trouble since then.

Here's my code snippet:

     public void GetFriendScores()
     {
         StartCoroutine (GetFriendsScoresCoroutine ());
     }
 
     IEnumerator GetFriendsScoresCoroutine()
     {
         Debug.Log("Started friends get scores coroutine");        
         
         //Assume these variables contain relevant information
         var ids = ............. (string list of facebook IDs)
                 
                 
         //Get a list of users who match the friend FB IDs
         var usersQuery = ParseObject.GetQuery ("FBUser").WhereContainedIn ("FB_ID", ids);
         
         //Use the user query result to find corresponding high score rows
         var scoresQuery = ParseObject.GetQuery ("HiScores").WhereMatchesQuery ("User", usersQuery);
         var scoresQueryTask = scoresQuery.FindAsync ();
         
         Debug.Log("Started get scores task");
         while (! (scoresQueryTask.IsCompleted))
             yield return null;
             
         Debug.List("Get scores task complete");
     }

The last line of Debug I see is "Started get scores task", and nothing after that.

When I run it in the editor, I get the correct data and the "Get Scores task complete" message.

Any idea what I might have missed? I'm using Parse 1.5.3 and can confirm that it was working before I re-wrote the code.