How am I supposed to win if my champ doesn't fight ?

I keep having this bug or whatever, that one champion doesn't fight in the game, even though positioned in the field, he just stand still, he also cant die, i lose while that one champ is still full HP and the other enemies also don't attack him, it's like he is not really there.

I have experienced this with: warwick braum garen

I lost quite some games because of this ...

I made a screenshot of one game:

https://i.imgur.com/AKkuPKs.jpg

you can see my warwick full hp just chilling there, after my blitzcrank died, the game was over, and warwick was just there full hp sleeping.