[GAMEPLAY] Mystical floating orb (visual bug)

During a bot game, I saw a flying orb in mid lane. It was doing nothing, shifting like Lux' E. As you can see in the chat, Lux couldn't see it, only me. It has once happened before in one of my games. I believe it has something to do with Challenging smite (in both games, there was a jungler with this type of smite). However, in this case, me, the jungler could see it, in the other case, my midlaner was the only one of our team that could see it. I have tried to reproduce the visual bug, but I have not succeeded (yet).

--edit: As soon as I took the screenshot, the orb disappeared. --