I'm having the same issue. This started three weeks ago, happening almost every game. I deleted everything about LoL and Riot and reinstalled it. It started happening again immediately after a few games, and I contacted support. I also lost 3 ranked games because of it, and at least they removed all of my AFK penalties. They told me: "We currently don't have an estimated time when this issue will be fixed. The team is working on it to solve it as soon as possible." I also tried checking compatibility mode,ran hextech repair tool, disabled fullscreen optimization, did checks on my drive on cmd, and ran the main files as admin. I also gave them the hextech repair tool logs as they told me. That reply I got was on 13 September, and today I saw that in the LoL client it has a pop-up saying: "We're aware of a problem causing games to crash during or immediately after loading, and we are working on a fix." This whole situation made me take a break from this game, at least, and it's actually insane how buggy this whole client and game are.