when I log in on a singleplayer world, my stuff is gone and my stuff in chests and furnaces too

Put the summary of the bug you're having here

I thought I would spawn with all my stuff and could just play minecraft.

what actually happened was, I was coming back in my world and everything was gone in my inventory and chests and storage.

Steps to Reproduce:
1. I made a world with the customize setting and made a home there in a mesa biome
2. than I made a redstone timer with a dropper connected to it and logged out.
3. than the other day I logged in again my stuff was gone and the timer was stopped.