This wasn't an issue with the previous versions of the beta, but when i downloaded the newest one. (with beacons and wither) the issue is with a random world (in other words a random world i created anytime before i downloaded the newest version of the beta) it will start to lag and then freeze up when walking (a rather short distance) in a certain (random) direction, or even looking in that direction. If you avoid walking or looking in that direction, the game works fine, this is very weird, i tried deleting the game and re-downloading it, also leaving and joining the beta many times including today. It effects random worlds (i have about 10) and most of which MOST are survival. It hasn't happened to a world created AFTER the new beta update, but as you can see this makes these world's virtually unplayable.