When I'm currently in the Nether the game will have moments of delay where every entity freezes but the player. Mobs will stop responding and sit at a stand still for at least 4 or more seconds, if I break any blocks in that period of time there's no animation to the block breaking and the block disappears but doesn't drop the item. Then everything catches back up and the animations and mobs start responding. But I can still move and walk about even though everything else freezes up. I also noticed that it doesn't happen in peaceful mode so it may have to do with the amount of hostile mobs and/or theirs a fault in the pathfinding algorithm in the hostile mobs. I did a little more testing and it looks like it has to do with large amounts of blazes all trying to path find to the player at once at blaze spawners. But if you're out of simulation distance the bug doesn't occur. So I guess if you want to replicate it try sitting at a blaze spawner in survival mode and make it so they can see you but can't reach you.