logging into a pre-existing world with no stuff

This has happened more than once, but sometimes when I log onto my 3+ year world, I start the game back at spawn with no items. I know I did not die before logging off, and usually, closing the game and reopening it fixes it. It is a 450 MB save file, so that could be a factor.

Also, this is just happening in my singleplayer world and not my realm.