Neighboring Houses show as Default/Empty

My best advice is to back up your saves regularly. The last time this happened to me, I had fortunately not saved more than 3 times so I was able to recover the last version before the corruption was triggered. For me, placing some RRs from the gallery caused this. Now that I'm not placing any RRs, I haven't seen this again. 

I have a dedicated folder in my documents for the save files with folders for each date. I don't back up the save every session, but about every week or so. That way, the worst case scenario is that I have to pull an older version to play the uncorrupted save again (albeit with lost progress) rather than losing it completely.