This is actually an old problem for me that goes back to the 1.8 and 1.9 versions of Minecraft.
What happened was I logged into 1.9 and changed many of my old command blocks to the newer type. The only problem was at the time I only had the 1.8 version of WorldEdit. So I opened my now 1.9 world in 1.8. This caused all the chunks with the new command blocks to be replaced with random new chunks, deleting all my command blocks.
I'm pretty good with command blocks but losing quite a few hours of work is a real pain in the neck.
It's been a couple months since then and I only thought of fixing it now. I find it unlikely, but I,d like to know if there is some way to revert back to a previous save in Minecraft?