[CLIENT] Freezes at loading screen

For three of my five most recent games, I've encountered this problem:

1. Enter Solo Queue for ARAM.
2. Wait 60 seconds as people reroll, choose summoner spells, etc.
3. Enter loading screen and watch as most people, including myself, load to 100%.
4. See that some people on both teams seem AFK (i.e., their champion picture doesn't display and they don't seem to be loading).
5. Alt+Tab out of the LoL client and exit.
6. Log back in and reconnect to game.
7. Load to 100% on my own.
8. Enter the game.

I'm not sure if this is a consequence of Patch 4.21, my computer, or my connection, but I was able to browse the internet while the LoL client was running. It also sometimes worked when I exited the LoL client and reconnected without logging out, but sometimes it didn't. I played three games on the first day and the problem occurred once, during the second game. I played two games two days later, and the problem occurred both times. There were also some other players who entered the games late, so I think this may be a common problem. Another, possibly unrelated problem, is that, one time during one of these games, the Howling Abyss loaded but none of the champions or the store were visible, though I was able to assign my abilities with Ctrl+(Q,W,E).