Android IL2CPP bulid crash MemoryStream deserialization

Hello! I'm developing casual game for Android and about to release first version.

But I stuck in terrible situation.

Google demand for 64bit apk, so I build as IL2CPP.

I get assetbundle from web server and it contains some binary data.

For binary data, I convert it as TextAsset.

Below is that code.

 private IEnumerator GetAssetBundle()
     {
         UnityWebRequest www = UnityWebRequest.Get(hNetworkManager.serverURL);
         yield return www.SendWebRequest();
 
         if (www.isNetworkError || www.isHttpError)
         {
             Application.Quit();
         }
         else
         {
             string assetBundleDirectory = Application.persistentDataPath + "/AssetBundle";
             string serialDataPath = Application.persistentDataPath + "/SerialData";
 
             if (!Directory.Exists(assetBundleDirectory))
                 Directory.CreateDirectory(assetBundleDirectory);
             if (!Directory.Exists(serialDataPath))
                 Directory.CreateDirectory(serialDataPath);
 
             TextAsset[] textAssets;
             AssetBundle assetBundle;
             hLevel.SerialData[] serialDatas;
             MemoryStream memoryStream;
             BinaryFormatter formatter;
 
             var studio = Instantiate(m_thumbnailStudio);
 
             byte[] data = new byte[www.downloadHandler.data.Length - head];
             System.Array.Copy(www.downloadHandler.data, head, data, 0, data.Length);
 
             File.WriteAllBytes(Path.Combine(assetBundleDirectory, "levels.unity3d"), data);
 
             assetBundle = AssetBundle.LoadFromFile(Path.Combine(assetBundleDirectory, "levels.unity3d"));
 
             if (assetBundle == null)
             {
                 //Debug.Log("Failed to load AssetBundle!");
                 yield break;
             }
 
             textAssets = assetBundle.LoadAllAssets<TextAsset>();
             serialDatas = new hLevel.SerialData[textAssets.Length];
 
             memoryStream = new MemoryStream();
             formatter = new BinaryFormatter();
             for (int i = 0; i < textAssets.Length; ++i)
             {
                 memoryStream.Write(textAssets[i].bytes, 0, textAssets[i].bytes.Length);
                 memoryStream.Position = 0;
                 serialDatas[i] = (hLevel.SerialData)formatter.Deserialize(memoryStream);
                 memoryStream.SetLength(0);
             }
             memoryStream.Close();
 
             var lastThemeColor = hColorManager.current.curColor;
             for (int i = 0; i < serialDatas.Length; ++i)
                 studio.SaveThumbnail(serialDatas[i]);
             hColorManager.current.SetTheme(lastThemeColor, true);
             hSharedData.Initialize(serialDatas);
             _loading.FirstLoading();
             #endregion
         }
     }

Up there "serialDatas[i] = (hLevel.SerialData)formatter.Deserialize(memoryStream);" line occur exception like this. and build setting. I also test Mono version and it worked properly.

I have no idea to solve this. PLEASE SOMEBODY HELP ME!