Have you tried my suggestion ?
There is already a thread for disappearing houses on existing saves, especially if they are huge but there is potentially a new issue since the temp saves files were moved to the AppData folder.
If it happens on a new save then that's more likely your issue then the existing one and another user had luck solving it with a new windows user (if that works, we can continue troubleshooting your old account, this is just for finding out what's going on).
If it's your existing saves only, could you send me your main one ? Upload to googleDrive, oneDrive, wetransfer or dropbox and DM me the link. If you have a backup from before they disappeared, that would be great as well.