Inventory is completely wiped after saving and logging off game and reappearing after 10 mins

This is the second world that I created on a private server with no one else having the ability to access my game.

 

I log out of the game and save. As I go back into the game a few days later, I am at spawn with nothing in my inventory. I did not die previously to leaving the game. 

 

This issue usually doesn't occur every time I log out, but seems to happen when I haven't logged into the game in a while.

Update: items seem to appear later on after playing for a while while without missing a beat. Very bizarre.