Entities in loaded chunks fail to save on exiting the world

I closed the Minecraft world, went to the main menu then turned off the XBox.

On reopening the world, all of the entities in chunks that were loaded were no longer there, and I could not bring them back by restarting Minecraft. 

All blocks that were placed and all items in my inventory were as they should be, and entities that were in unloaded chunks were still there.