Mobs go invisible & if monster you are attacked without any way of fighting back & usually you die if creeper or caught in confined space. Sometimes the mob is stuck in one place but is actually invisible & somewhere else as you can still see effect of mob in that they leave bubbles in the water & invisible sheep eat the grass. A creeper exploded in shallow water while looking at me & not moving at more than twiple  their normal detonation distance & the sound was loud and close but no damage I could see.  Often I am killed by invisible monsters & loose everything as when I go straight back my stuff is not there & only once did I recover it but it was outside on the other side of the wall when I was killed in a building with one opening & it was on the other side of the house. I'm constantly being blown up by invisible creepers even after sprinting out of the shelter & standing in the middle of a large empty space with no creeper in sight after doing a 360 sweep than BANG a hole is where I'm now standing in & a lot of health is gone. And if attacked by a zombie or spider you don't know what it is until you die & the pop-up tells you were killed by what ever invisible monster is attacking you.  At the moment if you have time it is best to exit to menu & restart before you get killed so got a chance to live & not loose everything like the diamonds you just got & is on the way to store it in the chest. The stuck mobs you can't harvest from e.g.. you can't sheer a sheep.