I do not usually meet bugs myself in game but this time I finally saw something really annyoing.
I played as ADC twice vs the same duo: Pyke and Yummi. I know that Yummi can be invisible with a champion that stays in stealth. While I was playing on lane, when she was attached to invisible Pyke, her Q became invisible as well. You could only see it in the last phase of casting - like a spark. It happened few times in 2 games. Check out my Jhin's games replay.