I have multiple accounts of this as well!
First time I was playing with my boyfriend and we were sitting next to each other and as soon as we got into champion select the entire interface was messed up. As soon as the banning phase was over it corrected, but the next time it happened his entire client crashed after picking a champion. We still got into game and he couldn't get in for about 10 minutes.
Today this happened to me too, proving that it isn't just his computer as mine is quite a bit newer and high quality and it NEVER lags or glitches. We got into champion select and I couldn't see my runes, masteries, summoner spells, ward skin or any of my teammates names. When I went to ban a champion, my client completely crashed and I lost LP for it. I did not leave the game nor did I refuse to pick/ban, so why should I be penalized?
There is also a bug with computers running Windows 10 where occasionally the client will not even open, resulting in a "pvp patch kernel not working" bug. However, if you run it as administrator it seems to work fine.