Mobs disappear close to the player

Mobs of all sort will vanish when I get within about 5 or 6 blocks from them. It started happening randomly after playing for a few hours, now every world is experiencing the same problem. Hostile mobs pop out of existence a few blocks away, but they can still interact with the player and attack. I tried to see if I could get all of the passive mobs in a farm I have to disappear at once but it kind of seemed like only a certain number stayed invisible at a time, with some popping in just as the others popped out. I have tried shutting it down and restarting, messing with graphics settings, and letting the console rest for a few hours but this is still happening across all my worlds, and needless to say its incredibly game breaking.

Update: Everything is back to normal again. I'm not really sure why, but then I guess I don't mind as long as it's working. The disappearing mobs kept up for about a day before it stopped.