Invisible Mobs

As it was, I was playing in survival mode. as my Laptop is very slow, I was playing on tiny render distance. but when playing, I was killed, while hunting enderman for their ender eyes, when I respawned, I spent a bit at my home, preparing to exact my revenge, and I was killed by a skeleton that walked right into my house. after I respawned again, the skeleton was gone, or so it seems, as I was getting shot out of nowhere. after being killed a few times, I saved/quit and rejoined, and found there was a skeleton. my items despawned, alas, but its a bug, nonetheless. this happens to all hostile mobs as I have tried.