Monster syncing fixes:

- clients freeze and disable AI characters if no updates have been received in a while (due to the monster being far away from player-controlled characters at the servers side for example)
- server disables AI characters that are too far for updates to be sent to clients (-> targets of monster missions can't swim away from the spawnpos and cause the clients' sonars to point to an incorrect position)

Subsurface/Source/Characters/AICharacter.cs

@@ -51,6 +51,22 @@ namespace Barotrauma
 
             if (Controlled == this || !aiController.Enabled) return;
 
+            if (GameMain.Client != null)
+            {
+                //freeze AI characters if more than 1 seconds have passed since last update from the server
+                if (lastRecvPositionUpdateTime < NetTime.Now - 1.0f)
+                {
+                    AnimController.Frozen = true;
+                    memPos.Clear();
+                    //hide after 2 seconds
+                    if (lastRecvPositionUpdateTime < NetTime.Now - 2.0f)
+                    {
+                        Enabled = false;
+                        return;
+                    }
+                }
+            }
+
             if (soundTimer > 0)
             {
                 soundTimer -= deltaTime;
@@ -149,11 +165,12 @@ namespace Barotrauma
         public override bool ReadNetworkData(NetworkEventType type, NetIncomingMessage message, float sendingTime, out object data)
         {
             data = null;
-            Enabled = true;
 
             //server doesn't accept AICharacter updates from the clients
             if (GameMain.Server != null) return false;
 
+            Enabled = true;
+
             switch (type)
             {
                 case NetworkEventType.KillCharacter:
@@ -198,6 +215,13 @@ namespace Barotrauma
                 case NetworkEventType.EntityUpdate:
                     if (sendingTime <= LastNetworkUpdate) return false;
 
+                    if (GameMain.Client != null)
+                    {
+                        lastRecvPositionUpdateTime = (float)NetTime.Now;
+                        AnimController.Frozen = false;
+                        Enabled = true;
+                    }
+
                     bool playerControlled = message.ReadBoolean();
                     if (playerControlled)
                     {