These missing chunks...
It might be error or you have did something to your computer data, you can fix it by going out of game, then going back in it...
They normally happen in servers...
Never happened for me in singleplayer...?
Normally theres 1/100 change to have missing chunk, happens more for laggy, and badders specs servers!
EDIT:
What is that block what has the brown sticky shape thing in it?:O