Sometimes the Portal just do not appear in underwater 3-x (trench) after the level has been be cleared, because there are some PortalPrevent(becomenemy) still in the level, and their creators(CustomObject) all have the same name variables WantEel and same visible variables false. im sure the reason of Portal not appear is that sometimes there is no any Floor's sprite_index is FloorTrenchB so WantEel will not become visible. It has already happened twice.
(sorry for that i couldn't upload any screenshots because some network reasons, and im not good at English so the logics and grammars of these statements are so broken)