My friends and I were building a minigame server. We started with a small platform and ended with a large one with bridges attached. Next morning my friend calls me up. He's on the Realm. He tells me that none of our work from the previous evening saved and that his name tag is gone (i.e., upon pressing Tab it shows his face but no IGN). I reverted to a backup, but only a few minutes later this happened twice more.

What I expected to happen:
The Realm would save our progress and we could continue in the morning.

What actually happened:
Realms saved none of our progress/

Steps to reproduce:
I'm afraid I don't know. As of now it only seems to happen at random with this particular world.