MAC CLIENT DOESN'T WORK AT ALL (CRASHES BEFORE GAME BEGINS)

I found my Mac Client started to have loading problem after the new patch 4.20 released, and my friends who are using Mac client has the same problem right now. the problem is that after the champion pick stage, everyone suppose get into a loading stage which is everyone wait until all people 100% loaded (10 champions icon will showed with players' name and the status of game loaded), the game will start, but my Mac client will frozen there and my screen will be total black and frozen, i can not even switch off and shut the system down on my desktop board. so i have to restart my computer over and over again. by now, i have tried the game spectating model, the summoners rift, Howling Abyss and customize game model, none of them have exception of loading game successfully, they all frozen on the loading stage. could Riot tech support team be ware of this serious problem, cuz many of my friend can not play any games within Mac client. thanks!