Items disappearing in chests and upon death

I was playing on Minecraft Realms and mining with a friend and she accidentally killed me with a stone pickaxe, and all of my stuff disappeared even though I was not close to any lava or cacti I lost all of my stuff. I was in a stone corner and the only I ended up getting back was my shield which disappeared soon after.

 

Also some of my stuff disappears in my chests, like when I close a chest to go open another one, and then come back, sometimes something random will disappear.