Help! The house I was building disappeared even though I saved.

I play the Sims only for the aspect of building houses as I do not care about the life portion. I have many different random lots filled with various houses I've spontaneously built and had fun with. Last night the idea struck me that I wanted to build a particular house in Del Sol Valley up in the 'rich people area'- Basically the mansions. Normally I usually kick out the resident living there. It was a single woman, Judith Ward, on the Ward Den lot. This was the one instance where I specifically did not kick out the resident and simply went into build mode directly.

I have a random sim I've chosen as my 'player Sim' but, again, I do NOT play the game for the life aspect. I had my original Sim living in a house but since it took unfathomably long to load I booted them out of their own home so that it would just kick me to the various maps at the start for easier access. This worked great and I have actually constructed many properties since doing this and they've been fine, so clearly this is not the problem.

But I did not begin to 'play' as Judith Ward nor do I care to. I usually evict them and bulldoze the lot but I had decided not to do that this time as I figured it wouldn't make a difference and that the Sim would simply 'put up' living there as an NPC regardless of the level of construction. I bulldozed her mansion and I began to work for multiple hours in constructing what I wanted to instead. Even after many hours I still only had the 'bare bones' of what I wanted as there were only walls, doors, and staircases. I planned on working on it more soon as it takes me a lot of time to pour into this and this was a big property. I, 100% without even a question about it, saved last night before exiting my game.

So imagine my surprise when I wait for the long loading time and finally get over to Del Sol Valley and I catch a glimpse of NOT the house I was constructing up on the hill. I thought, "...I didn't put a roof on yet. Why is there a roof? That's not my house." as I was still constructing it and it doesn't even have basic functionalities like a toilet, kitchen, or etc. I click on it and wait for the load time once more. Eventually when I get in it shows me the OLD property as it once was, The Ward Den, fully restored and no hint of my home that I was working on whatsoever.

Understandably I'm very upset and mad over this. I spent many hours laying out the new mansion in its place. Could not booting the resident actually completely make whatever I put there obsolete? If so, isn't that a MAJOR oversight? Why would not evicting the one resident delete my progress that I saved? That is the ONLY thing I did different. Would not having a bathroom, kitchen, or anything that a person might need be a reason why the house disappears? I really don't understand this at all.

And before you ask...
• No I am not playing with any crazy mods. I don't even use CC. Just packs I've purchased. I'm on the PC.
• YES! I did save. At the time of saving the property only had walls, doors, an elevator, and staircases. Nothing else.
• No! I did NOT save the home to 'My Library' as it wasn't complete yet and still in the process. I figured a regular save was 'enough'.
• It is Del Sol Valley, The Ward Den lot. Judith Ward was the Sim and she was not my active sim nor have I ever played her. I simply wanted her lot.
• I did not evict the resident in the home before building. I just went straight to build mode and carried on.
• I do have a 'life sim' but I never play the life aspect of the game. I have constructed many houses before now with no issues.
• I DID try and look online to see if anyone had any similar problems and I could find none even close in my search.

I would like to know why this house is gone. Must I always evict the resident before proceeding? And why is not evicting a random resident so game-crashing as to delete all progress if that is the case? I'm really mystified by this and upset at my lost progress. I tried to look for a similar issue online but no one had this problem. I don't like the idea of having to rebuild but at this point I don't think I have any other choice. Could anyone help me?