This has happened to me twice while playing Minecraft multiplayer (not on a realm or sever) where I have gone through a portal and proceeded to die in under a second with the death message of falling out of the world and when I go back through the portal (it worked fine every other time) none of my items were there. This has happened when I have gone through a nether portal and a end portal. I have lost several hour of gameplay due to this.
I was not using any mods or Addons only texture packs