Almost every game I've been in on PBE, there's at least 1-2 AFK's and Im assuming it's because of the client bugging out. It's been happening to me too and it's irritating. It's usually near the beginning of the game and if people actually left in the beginning of the game that's really weird because why would you queue up in the first place :/
Honestly the client sucks right now, just bugged me out again = movement delay, disconnected chat, etc. I had to restart the whole client which took about 6 min, leaving a game for 6 min. My wifi is completely fine.