I have run into several situations where I hear/see a hostile mob, in the distance, and it never attacks me.  I shoot an arrow and it seems to go right through it.  When I get up close to it, it still does not attack.  When I hit it with a sword, it's like it isn't there and nothing happens to it.  It will say there and growl (if the mob is a zombie) and make all of its normal noises, but it never attacks and no attack on it does any damage.  I even minded the stone around a zombie, yesterday, and it stayed right where it was before I took the stone out.  I'll attach screenshots for that.  Also, I noticed that when I was in a village, at bedtime, a villager was laying, diagonal, with their feet at the foot of the bed and their body in open air, over the floor.  I walked close to him and he floated up through the ceiling.  Next, as I went upstairs in my house, I saw him laying on the floor, on the next floor up.  And, on the way up the stairs, there was a younger villager laying in the air, over the stairs.  When I went to approach the villager on the floor, on the next floor, as I got close to him, he moved--still lying down–through the air, like magic, and landed perfectly in one of the upstairs beds.  Wasn't able to capture photos of the weird position downstairs or when he was laying on the floor, but I did get a screenshot of the young one over the stairway (and the baby zombie I referred to, earlier).

Also, with regards to the zombie that didn't move–after I explored, further, into the cave where I encountered him, I came back and he was gone.  Next thing I know, I'm getting hit, out of nowhere, and there's no mob or lava or anything else that could cause me pain.  I quickly backed up to see if I could see what it was that was hurting me.  I couldn't see anything, so I moved forward again and again was attacked.  I walked further into the cave and all of a sudden was getting heavily attacked.  The attack reminded me of a young zombie–that vicious, all-out, crazy attack they do.  Then I realized–I was probably now fighting the little zombie I saw earlier.  Only now he wasn't stuck and he was INVISIBLE! AAAAAHHH!!Unable to render embedded object: File (  Anyway.  I've attached a few screenshots.  Please let me know if you need any more input from me.  Thanks) not found.