I was in my Minecraft World and I picked up my shulker box (Netherite and Ancient Debris) and entered the nether. When I emerged the system glitched and kicked me out when I reenter, that shulker box was gone. Other items were in my inventory, just not that. I have a copy of my world, but it was pre-1.17 and I have collected new blocks and did some modifications to my building.