Delay in visibility of Pink wards

When i facecheck brushes pink wards might not be visible for several seconds. It might appear last 0,00001s before i leave the brush. Or It might not appear after i enter and leave it at all. It might not appear even after several seconds of standing there. I think 3-4 seconds was the biggest delay i ever got on this. You enter - Oh there is nothing here. And when you already leaving this motherfuckers pops up behind you. And you have to walk back. I have no idea if this is intentional or not but i get this every game. There is no similar problem with champions visibility.