Lag issue from open mastery prior to game start?!?

Recently I've been lagging hard going into a game where I'm changing masteries in the lobby and the game starts while I'm still making changes, the mastery page when I alt+tab shows up even though I'm in-game and my ping is ridiculously high. After I restart the client completely and reconnect the lag goes away, I was able to repeat this process multiple times, not sure if it has anything to do with the mastery page still showing even after the game launches but that's the only time my ping skyrockets.

Is anyone else running into a similar issue or can try to do the same thing to see if it's an actual bug? As it occurs just about every time my mastery page seems to get stuck after the game launches.