I started a survival world, multiplayer enabled. When we got to create a portal and went in it, 

it made the whole world lag (mob stopped moving, couldn't open chest or doors, couldn't return back) but players are still able to move. When I quit the app and reopen it, I spawn a few block besides my portal out of the nether. I'm the host of the world and if someone else goes in the nether without me, it's fine... I also can't access the pause menu when the world lags, so I have to force quit Minecraft PE and re enter. Can someone help me fix this?