Basically, when there's some bones and arrows in my inventory or a chest, a random item disappears completely, irrespective of its number. This issue happens sometimes and not always, hence why it is difficult to attach a video or to replicate it. It happened to me once, twice to my sister, and a bunch of times to my friends. My friends lost things like a used bow (unenchanted), string, a bucket of water, etc. As for me and my sister, we both lost a heavy core (in the same world) and she lost 40 cooked chicken (in a different world) that she had in her inventory with the bones and arrows. This happens when we have the bones and arrows in the same storage unit (so the same chest or inventory). Some of the arrows and bones disappear with a random item. The number of bones and arrows required for it to happen is also random i think. Sometimes, we just raided skeleton spawners so we had stacks of bones and arrows. And sometimes, just 20-30 of each. The quantity of the disappearing object doesn't seem to matter: 1 heavy core from my chest (mine), 1 from her inventory (hers), 40 cooked chicken from her inventory, etc.