Couldn't barely control my champ in league game

Just played a yi game where I was fine at the start, but about 9 minutes in I started getting large delays between my clicks and champ response. These eventually grew to be as long as 40 seconds at times where my champ would just stand there. I could see everything going on, my ping didn't spike, and my champ didn't run back to fountain, but I could not move. Never seen this before in my life, as far as I know my internet was fine the whole time, I tested it on youtube and saw no problems. ATM a few minutes after game my speeds fine.