I made a Minecraft world and built a volcano which I was quite happy with. Then I tried to use a command block to create flame particles on top of it, just for a finishing touch. I used the command
/particle flame coordinates coordinates2 0.5 300000. I set the command block to always active and repeat, which was an absolutely pathetic idea. The world froze completely. I thought maybe I could change the version of the game to 1.9, as repeat CBs weren't implemented yet, then. When I logged in, everything was fine, other than the fact that a whole chunk of the build was gone, just gone. I did some research and I found out that I could use NBTExplorer to disable command blocks, and I did so. When I logged on my 1.11 user, the world was still in 1.9, and the chunk was missing. I quit the world and relogged, and it said that the world was in 1.11, but the chunk was still gone.
Firstly, what in the world have I done? Secondly, what can I do, if anything, to fix my slightly embarrassing problem?