fix

Only the spawn authority should reset the sent time and reset the dirty flag for NetworkList changes to avoid sending both the CreateObjectMessage (which would contain the changes) plus the NetworkVariableDeltaMessage.

Author: NoelStephensUnity

com.unity.netcode.gameobjects/Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -61,10 +61,12 @@ public NetworkList(IEnumerable<T> values = default,
         internal override void OnSpawned()
         {
             // If we are dirty and have write permissions by the time the NetworkObject
-            // is finished spawning (same frame), then go ahead and reset the dirty related
-            // properties for NetworkList in the event user script has made changes when
-            // spawning to prevent duplicate entries.
-            if (IsDirty() && CanSend())
+            // is finished spawning (same frame) and the instance is on the spawn authority
+            // side, then go ahead and reset the dirty related properties for NetworkList
+            // in the event user script has made changes when spawning to prevent duplicate
+            // entries (i.e. they are sent via CreateObjectMessage so we don't need to send
+            // the NetworkVariableDeltaMessage.
+            if (IsDirty() && CanSend() && m_NetworkBehaviour.HasAuthority)
             {
                 UpdateLastSentTime();
                 ResetDirty();