When I started a new world on November 30, I started out normal. Eventually, I made an armor stand, and put my armor on it (of course). After a couple times of taking it off to go mining, I came back and saw that it was missing.

Put the summary of the bug you're having here

What I expected to happen was when I came back, I expected the armor stand to still be there, not having just vanished into thin air.

The thing that actually happened was I came back to my house, which was actually just a 5x5 little hut with no roof and one door, and it was just missing, nowhere in my chests or anywhere on the ground.

1: My guess is to craft the armor stand, because otherwise it wouldn't be the bug.
2: I went mining, a couple hundred blocks or so away from my house.
3: I came back and my armor stand was missing, along with the pumpkin I put in place of the helmet I hadn't crafted yet.