fix

This resolves the issue with the new edge case where a scene could be unloaded but a spawned object referencing the scene handle could still be spawned (pending being de-spawned within a few frames).

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/Core/NetworkObject.cs

@@ -3420,15 +3420,14 @@ internal void SceneChangedUpdate(Scene scene, bool notify = false)
             {
                 // Since the authority is the source of truth for the NetworkSceneHandle,
                 // the NetworkSceneHandle is the same as the SceneOriginHandle.
-                if (NetworkManager.DistributedAuthorityMode)
+                if (NetworkManager.DistributedAuthorityMode && NetworkManager.SceneManager.ClientSceneHandleToServerSceneHandle.ContainsKey(SceneOriginHandle))
                 {
                     NetworkSceneHandle = NetworkManager.SceneManager.ClientSceneHandleToServerSceneHandle[SceneOriginHandle];
                 }
                 else
                 {
                     NetworkSceneHandle = SceneOriginHandle;
                 }
-
             }
             else // Otherwise, the client did not find the client to server scene handle
             if (NetworkManager.LogLevel == LogLevel.Developer)