diff --git a/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs b/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs
index e5b1ca749fc..0bbf9620970 100644
--- a/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs
+++ b/shadowsocks-csharp/Encryption/MbedTLSEncryptor.cs
@@ -118,11 +118,6 @@ public override void Dispose()
             GC.SuppressFinalize(this);
         }
 
-        ~MbedTLSEncryptor()
-        {
-            Dispose(false);
-        }
-
         protected virtual void Dispose(bool disposing)
         {
             lock (this)
diff --git a/shadowsocks-csharp/Model/Configuration.cs b/shadowsocks-csharp/Model/Configuration.cs
index 3c0a79a38e9..d5b0e1c56c1 100755
--- a/shadowsocks-csharp/Model/Configuration.cs
+++ b/shadowsocks-csharp/Model/Configuration.cs
@@ -150,6 +150,7 @@ public class Configuration
         private LRUCache<string, UriVisitTime> uricache = new LRUCache<string, UriVisitTime>(180);
 
         private static string CONFIG_FILE = "gui-config.json";
+        private static string CONFIG_FILE_BACKUP = "gui-config.json.backup";
 
         public static void SetPassword(string password)
         {
@@ -560,6 +561,20 @@ public static void Save(Configuration config)
                     sw.Write(jsonString);
                     sw.Flush();
                 }
+
+                if (File.Exists(CONFIG_FILE_BACKUP))
+                {
+                    DateTime dt = File.GetLastWriteTimeUtc(CONFIG_FILE_BACKUP);
+                    DateTime now = DateTime.Now;
+                    if ((now - dt).TotalHours > 4)
+                    {
+                        File.Copy(CONFIG_FILE, CONFIG_FILE_BACKUP, true);
+                    }
+                }
+                else
+                {
+                    File.Copy(CONFIG_FILE, CONFIG_FILE_BACKUP, true);
+                }
             }
             catch (IOException e)
             {
diff --git a/shadowsocks-csharp/Model/ServerSpeedLog.cs b/shadowsocks-csharp/Model/ServerSpeedLog.cs
index 7f4ed1df3f8..69a0c21eeff 100644
--- a/shadowsocks-csharp/Model/ServerSpeedLog.cs
+++ b/shadowsocks-csharp/Model/ServerSpeedLog.cs
@@ -432,6 +432,12 @@ protected static void UpdateTransLog(List<TransLog> transLog, int bytes, DateTim
                 const int base_time_diff = 100;
                 const int max_time_diff = 3 * base_time_diff;
                 int time_diff = (int)(now - transLog[transLog.Count - 1].recvTime).TotalMilliseconds;
+                if (time_diff < 0)
+                {
+                    transLog.Clear();
+                    transLog.Add(new TransLog(bytes, now));
+                    return;
+                }
                 if (time_diff < base_time_diff)
                 {
                     transLog[transLog.Count - 1].times++;
diff --git a/shadowsocks-csharp/Obfs/AuthAkarin.cs b/shadowsocks-csharp/Obfs/AuthAkarin.cs
index 11386fa57cd..0391e803220 100644
--- a/shadowsocks-csharp/Obfs/AuthAkarin.cs
+++ b/shadowsocks-csharp/Obfs/AuthAkarin.cs
@@ -62,6 +62,15 @@ public override Dictionary<string, int[]> GetObfs()
             return _obfs;
         }
 
+        protected override void Disposing()
+        {
+            if (encryptor != null)
+            {
+                encryptor.Dispose();
+                encryptor = null;
+            }
+        }
+
         public override object InitData()
         {
             return new AuthDataAesChain();
@@ -167,17 +176,13 @@ public void PackData(byte[] data, int datalength, byte[] outdata, out int outlen
             {
                 byte[] rnd_data = new byte[rand_len];
                 random.NextBytes(rnd_data);
-                encryptor.Encrypt(data, datalength, data, out datalength);
                 if (datalength > 0)
                 {
+                    encryptor.Encrypt(data, datalength, data, out datalength);
+                    Array.Copy(data, 0, outdata, start_pos, datalength);
                     if (rand_len > 0)
                     {
-                        Array.Copy(data, 0, outdata, start_pos, datalength);
-                        Array.Copy(rnd_data, 0, outdata, start_pos + datalength, rand_len);
-                    }
-                    else
-                    {
-                        Array.Copy(data, 0, outdata, start_pos, datalength);
+                        rnd_data.CopyTo(outdata, start_pos + datalength);
                     }
                 }
                 else
diff --git a/shadowsocks-csharp/Obfs/AuthChain.cs b/shadowsocks-csharp/Obfs/AuthChain.cs
index ceeb13ada76..8a40a3b7750 100644
--- a/shadowsocks-csharp/Obfs/AuthChain.cs
+++ b/shadowsocks-csharp/Obfs/AuthChain.cs
@@ -103,6 +103,15 @@ public override Dictionary<string, int[]> GetObfs()
             return _obfs;
         }
 
+        protected override void Disposing()
+        {
+            if (encryptor != null)
+            {
+                encryptor.Dispose();
+                encryptor = null;
+            }
+        }
+
         public override object InitData()
         {
             return new AuthDataAesChain();
diff --git a/shadowsocks-csharp/Obfs/ObfsBase.cs b/shadowsocks-csharp/Obfs/ObfsBase.cs
index d17446ae9e8..b9e970aef18 100644
--- a/shadowsocks-csharp/Obfs/ObfsBase.cs
+++ b/shadowsocks-csharp/Obfs/ObfsBase.cs
@@ -116,8 +116,14 @@ protected virtual void Dispose(bool disposing)
                     return;
                 }
                 _disposed = true;
+                Disposing();
             }
         }
+
+        protected virtual void Disposing()
+        {
+
+        }
         #endregion
 
     }
diff --git a/shadowsocks-csharp/View/LogForm.cs b/shadowsocks-csharp/View/LogForm.cs
index 8919bdc5f7c..f48b8803e5f 100644
--- a/shadowsocks-csharp/View/LogForm.cs
+++ b/shadowsocks-csharp/View/LogForm.cs
@@ -113,7 +113,9 @@ private void ReadLog()
             catch (FileNotFoundException)
             {
             }
-
+            catch (ArgumentNullException)
+            {
+            }
             Text = $@"{I18N.GetString("Log Viewer")} {_currentLogFileName}";
         }
 
diff --git a/shadowsocks-csharp/View/ServerLogForm.cs b/shadowsocks-csharp/View/ServerLogForm.cs
index bb53e3a9292..69f9c907c54 100644
--- a/shadowsocks-csharp/View/ServerLogForm.cs
+++ b/shadowsocks-csharp/View/ServerLogForm.cs
@@ -258,7 +258,7 @@ public void UpdateLogThread()
             {
                 Configuration config = controller.GetCurrentConfiguration();
                 ServerSpeedLogShow[] _ServerSpeedLogList = new ServerSpeedLogShow[config.configs.Count];
-                for (int i = 0; i < config.configs.Count; ++i)
+                for (int i = 0; i < config.configs.Count && i < _ServerSpeedLogList.Length; ++i)
                 {
                     _ServerSpeedLogList[i] = config.configs[i].ServerSpeedLog().Translate();
                 }