Blocks become invisible and items start flickering after I die.

I was playing on a hardcore world that i spent alot of time on and died to a creeper sadly. When i went into spectator mode my items would flicker and blocks would turn invisible. This would happen on every world except the blocks didnt vanish which I think is another bug on its own. If I would be playing on multiplayer and i would die. the items would still be there but i cant pick it up and every mob would just freeze in place and i wont be able to see players.