i was mining underground and was killed by some skeletons and when i went back down my items were all invisible (when they went back into my inventory i could see them again) and i was shot by invisible skeletons (i could see the arrows though)

to reproduce just

1.get killed by a mob while holding items (preferably near spawn)
2.go back to where you died before the mobs and items despawn
3.you should be unable to see the items and the mobs