Read files from LAN folder using StorageFolder.GetFilesAsync returns folders but no files

Question

I'm trying to write a basic UWP app to stream media over a LAN via DLNA. I have three PC's on the same LAN, all running W10 Pro, a Homegroup set up, Media streaming switched on and configured on all of them but when I run the method below, passing in a remote folder all I get in folders back and no files, even though I know the folders contain files.

async private void LoadMediaFiles(StorageFolder mediaServerFolder)
    {
        try
        {
            MediaFolders = await mediaServerFolder.GetFoldersAsync();
            MediaList.Items.Clear();
            if (MediaFolders.Count > 0)
            {
                MediaList.Items.Clear();
                foreach (StorageFolder folder in MediaFolders)
                {
                    MediaList.Items.Add(" + " + folder.DisplayName);
                }
                MediaTitle.Text = "Media folders retrieved";
            }

            var queryOptions = new QueryOptions();
            var options = new QueryOptions();
            options.FileTypeFilter.Add(".avi");
            options.FileTypeFilter.Add(".mp4");
            options.FileTypeFilter.Add(".mkv");  
            options.FileTypeFilter.Add(".wmv");
            options.FolderDepth = FolderDepth.Deep;
            var queryFolder = mediaServerFolder.CreateFileQueryWithOptions(queryOptions);
            MediaFiles = await queryFolder.GetFilesAsync();

            if (MediaFiles.Count > 0)
            {
                foreach (StorageFile file in MediaFiles)
                {
                    MediaList.Items.Add(file.DisplayName);
                }
                MediaTitle.Text = "Media files retrieved";
            }
            else
                MediaTitle.Text = "No files found";
        }
        catch (Exception ex)
        {
            MediaTitle.Text = "Error locating media files " + ex.Message;
        }
    }

To get the known DLNA servers I use:

IReadOnlyList<StorageFolder> MediaServers = await KnownFolders.MediaServerDevices.GetFoldersAsync();

and then list the folders from the selected server. When the user taps on any folder it calls the above method but I never get files, only folders.

I can stream between each of the PC's no problem using WMP or VLC etc, it's only trying to get media files via UWP to stream that it doesn't work... I just get "No files found" on every folder.