Realm deleted part of building

I play a 10 person realm with a few friends. Two of us play on Switch, the others on pc. Today I logged in to find the top of one my builds partially deleted. After looking through my backups it's been like this for at least a week. I hadn't noticed because I spent all of that time mining deep underground, directly below the build.

I can't use one of the backups because it would take less time to just rebuild then it would to repeat all the other progress we've made.

Is this a common issue? Is there a way to prevent it from happening again? Or is this a sign of Realm corruption? Would it be best to reload one of the backups?