Logged onto my Realm that I've been playing with friends for the past five months. I spawned at our default spawnpoint, instead of where I last logged off, with my inventory wiped. When I walked to where our base normally is, it looked like the whole area was never touched, with the exception of a few structures still in tact near the default spawn area.

I was playing last night with no issues. My friend, the owner, played this morning with no issues. It wasn't until I logged on a few minutes ago that almost the entire world was restored to its untouched state. Something must have happened in those few hours.

Our most recent backup from four hours ago had this same problem. Luckily, the owner had a backup of the world from 18 hours ago. Everything is now back to where it was at that time.

What could have happened?