Despawning Fences and items alike.

Been working on my town for a few days now and ive noticed that a large ammount of fences and other details keep disapearing. It shouldent be grief as its 1 fence or 1 block at random locations.
any idea what the problem is? "build is in builder world"

 

Think i found the problem. should have been when some we was done close might be wrong thought.