Had this issue too. It was on a server (hasn't happened yet in single player), the server probably didn't have lag because it was new, I could see my body, but couldn't open it or hit it, couldn't see the hitbox either. This happened on 2 occasions.
That is a different, temporary issue. I had it happen to me once, all I did was walk away and do something else for a few seconds, when I came back I could loot it.