So I tried to do something funky. I logged in and entered my survival world and went AFK fishing for a while. Then, I joined the same world via the Singleplayer HUD, but with a different account, and then logged out after moving places for about 30 seconds. When I tried saving the world after an AFK session that day, it takes noticeacbly longer time to do so compared to previous performances. The next day, when I joined that world again, I found... this.

I know this isn't how I am supposed to play the game, but... yea.