Door disappearing in spawn chunks

I am in my spawn chunk, I have opened to lan. I made a portal to the nether and i went in with another player on the exact same snapshot as me. when we both came back, we couldnt see the door or find the hitbox. We kept on replacing the door but it kept on disappearing. we decided to break the obsidian to see what would happen but nothing changed. Today, when i logged in, (not a lan anymore, just playing by my self) I couldnt find the door again.

Note:
I have a mac book air.
I do not use any texture packs mods etc.
No commands were used.