update & style

Adding change log entry.
Fixing some typos.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -26,6 +26,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+- Fixed issue where either an `AttachableBehaviour` or an `AttachableNode` can throw an exception if they are attached during a scene unload where one of the two persists the scene unload event and the other does not. (#3931)
 - Fixed issue where attempts to use `NetworkLog` when there is no `NetworkManager` instance would result in an exception. (#3917)
 
 ### Security

com.unity.netcode.gameobjects/Runtime/Components/Helpers/AttachableBehaviour.cs

@@ -245,7 +245,7 @@ protected override void OnNetworkPreSpawn(ref NetworkManager networkManager)
             IsDestroying = false;
             // When attached to something else, the attachable needs to know if the
             // default parent has been destroyed in order to not attempt to re-parent
-            // when detached (especially if it is being detatched because it should be destroyed).
+            // when detached (especially if it is being detached because it should be destroyed).
             NetworkObject.OnDestroying += OnDefaultParentDestroying;
 
             base.OnNetworkPreSpawn(ref networkManager);
@@ -260,9 +260,13 @@ private void OnDefaultParentDestroying()
                 return;
             }
             IsDestroying = true;
-            // Just destroy the GameObject for this attachable since
-            // the associated NetworkObject is being destroyed.
-            Destroy(gameObject);
+            // If not completely detached, then destroy the GameObject for
+            // this attachable since the associated NetworkObject is being
+            // destroyed.
+            if (m_AttachState != AttachState.Detached)
+            {
+                Destroy(gameObject);
+            }
         }
 
         internal override void InternalOnDestroy()
@@ -319,7 +323,7 @@ public override void OnNetworkPreDespawn()
         }
 
         /// <summary>
-        /// This will apply the final attach or detatch state based on the current value of <see cref="m_AttachedNodeReference"/>.
+        /// This will apply the final attach or detach state based on the current value of <see cref="m_AttachedNodeReference"/>.
         /// </summary>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private void UpdateAttachedState()