Invisible Cho'Gath - Gameplay

I just had a game where I could not connect right away and had to reconnect to the game. Afterwards once we loaded in two of the chapions on the other team were invisble "Darius and Cho'Gath". I could see them chat in the game but with a bright green text with no champion assignment and my other team mates could see them normally. Also in-game portraits such as tower destruction or kills were nothing more than a green box when they were involved.

1.) I cannot replicate this. 2.) This is the only time it has ever happened to me.