Game just completely broke

So, I was playing a game no problem. The game finished, and I immediately went to start another. I made it through Champ Select, no problem. The second my game tried to load, I was faced with a black screen and "League of Legends has stopped working". Ok, no problem, restarted the entire client. This time: "You have disconnected. Check your internet connection and try again". I went into task manager, ended all league-related processes and restarted the client. "You have been downgraded to an older version of League of Legends. Please wait while we patch you up to the latest version." It worked, and I finally got in just as the remake vote started. Our team remade, the end. My question is, what causes the game to break like this? I wasn't even using any custom skins this time.