When I'm playing on a friends world, and they start typing in chat, every thing in the game other than my movement visually freezes. This includes mob movement. So if you are for instance, fighting a hostile mob without the other player knowing, the mob just freezes, but its "code-movement" doesn't freeze. So a situation could play out like this. I'm fighting a zombie, and it stops moving, I know my friend is typing, I'm doomed I think while I wait for my friend to stop typing. Then suddenly, I just die. This situation is even worse if there are multiuple enemys coming after you. This does not happen when you are playing on servers or realms, only if you are playing on a friend world. This also effects block breaking and pleacing. So if I was breaking blocks, they would just reappear once my friend is done typing. And if I was placing blocks, they would disappear once my friend is done typing. There are many other game-breaking and annoying things with this. But the ones I just listed are the problems that make the game the most un-playable. I (and probably many others) hope this gets fixed soon.