Call me paranoid
But I feel like there's a 12 hour reset or something on the matchmaking. If I only play one ranked game a day, my chances of winning (apparently) increase dramatically. I'd say I win 75% of the first games. But if I stupidly play multiple ranked games in a row - lets say 3 - I'm almost guaranteed to lose the second and it's a true gamble on the third one.
It's odd to me that if I play 3 ranked games in a row its a total shitshow. But if I play 3 ranked games in as many days, it's a high likelihood for 100% winrate. Combine this with the fact that one of the LoL tip instagram accounts mentioned you have the best chance of winning you're first match of the day, I'm starting to think the game says "Oh hey, this guy's pretty good! He can definitely carry those bums waiting to play - group 'em together and spread the love around!"