Mobs making the game crash

For the Minecraft Better Together version,

I found that when there is an abundance of mobs or monsters in one area, it causes the game to lag very bad until it is frozen or the character cant move (almost like having very low FPS). An example would be my zombie spawner (mob farm) and skeleton farm, when after a lot of mobs accumulate into one space, the game lags to the point it is frozen or cant move!