Laggy Client

Pre-game during champ select, last 10 seconds before picking or banning a champion the client becomes laggy, as in slow to respond. So as I type in Zyra in order to ban, the client takes 7+ seconds to react, causing me to be kicked for failing to lock in a ban. Also a problem in post game, where it takes almost a full minute to reach post-game screen from the time I see "Victory/Defeat" at end of game. Delayed to point where everyone is out of post game lobby. Why does the client take so long to respond to every command once in a lobby?