chore: added fixme comment

Engine.Core/Systems/UniverseEntranceManager.cs

@@ -16,6 +16,9 @@ public class UniverseEntranceManager : Internal.BehaviourIndependent
 
     protected override void OnEnteredUniverse(IUniverse universe)
     {
+        // FIXME: This causes an issue when the UniverseEntranceManager is already attached to a UniverseObject then registered into a Universe,
+        // the enter/exit universe collectors call OnUniverseObjectRegistered internally on Assign, but since the Universe calls the OnUniverseObjectRegistered
+        // event it tries to call OnUniverseObjectRegistered again on the same object, causing a duplicate entry error.
         enterUniverses.Assign(universe);
         exitUniverses.Assign(universe);