The back and forth lag with the new Rift.
Back when the new Rift was first released for Team Builder, everyone knew of the lag problems. The boards here were flooded with people complaining about fps drops, ping spikes, yada yada. Shortly after, Riot fixed the problem and there was little to no lag to be had. Well, after this 4.20 patch, the lag is back to just as bad as it was, if not worse. Many of the people I've played with have noticed this, and it's rather gamebreaking to be forced to stand still because it won't respond to clicks and whatnot. I've lost a few games because I'd go to chase down an almost-dead opponent and have lag kick in, and they kill me at full health rather than me knock down the last few hits on them. They end up fed. Game over. What I'm trying to say is that whatever Riot did last time to fix the problem needs done again. I get that post-patch there were a lot of bugs and problems, but slow store loading times is a bit less important than in-game lagging.