Armor dissappears when you die

When you die soo fast or with very much lag, the game just make your armour or the object you had in your hand.

It not happens every time. In my case I losted two times when I hit a wall going with elitras and fireworks and one when a wither skeleton spawned by the wither killed me when the world was soo lag because of the amount of blocks that the wither destroyed.