Three times this has happened. A section of placed blocks/items disappear. The 1st time times it was a section of fencing. The 2nd time it was a different section of fence, you can see that in one of the screenshots. It was a sheep pen where I had about 30 sheep and a section of fence disappeared and all the sheep got out. The 3rd most recent time it was a room in my castle. This time it was at least 20-30 blocks that disappeared. That's in the other screenshot. This is a single player game on Windows 10 edition. I don't know if my world is just corrupted or if it's a bug.