This really shouldn’t happen, at least give us a warning or the possibility to save the house before deleting it. Gladly, I did save and was able to load an older save, but not all players are that lucky and loose their houses they’ve built hours and days on.
I think it’s always been like that, at least in my game. I’ve always thought it was a mistake by the developers. If a house interests me, I save different versions as it changes over time, so I can recover it if there’s a change in inhabitants.
I had this happen to me in Dowon, for the 100k lot near Hwang Park. Built a nice house to buy for my zoi down the line. Completed it, saved and backed out to map. Instantly it was replaced with the pre-built, so its definitely all cities. Can’t wait till its fixed woooot!