I spawn floating, I can only see the skies and players but flickering

I'm using 0.12.2 Alpha
Everytime I connected to a Server, I keep spawning in the skies floating and what I only see are the skies and the players which are flickering when they started to move. And if I did /spawn, my game will start to flicker aswell.
But the game works fine in the single player.

Update:
I uninstalled and install the Game.
Now I can't even connect to a server.
Stuck in the Generating World Locating Server screen.