Leaverbuster punished me for leaving games even though i never left one

I played one ranked game before my class (no punishments or anything prior to this game), and when i came back, i got punished by the leaverbuster system for leaving games, yet i never left a game and never went afk. I was playing as thresh and never once sat at the fountain afk or left the match. After i came back from my class i got the punishment and now have to wait 5 minutes before every que.

But i never went afk or left the game!! Why did i get this punishment?!?!?!

And i NEVER got any type of warning prior to this punishment telling me that i had done something wrong.

The last time i left a game was back in December but it was only 1 game that i left