Champion Select Bugs a plenty
Play a lot with my friends and seems like at least one every few games someone has some major problem with the client. Pretty sure we all run 64-bit Windows 10 with new client (which is obviously a mistake). Sometimes I get bug splats in the champion select, screen goes black for about 15 seconds and then I'm back in with 10 seconds or so to pick my champion. Sometimes you can change runes or mastery but you can't select a champion or change your summoners inevitably leading to queue time out or penalty. Sometimes when we try to log back in after any of these happen, you can't type your password in to log back in and you have to keep reloading it.
Just putting this here before we all pretty much go back to using old client, I've wanted a new client ever since Oct 2011 when the game was totally unplayable seemingly because of the adobe air client, but this execution should've never seen a release. The UI and UX is totally out there in terms of user-friendly layouts, the bugs have been so numerous that it's amazing it got past early stages of release.