Yes, I had tried opening older saved files with the same home, but the issue was still ongoing. I just decided to build the home all over again and saved it to my gallery just in case. I think the issue was that the game was confusing my residential lot as a residential rental.
I noticed this when I clicked on rooms on the new home I built, and it gave me the pop-up to designate the room to a specific household (even though it was just a residential lot??).
My first save with the second home disappeared again, but luckily, I had it in my gallery, and I just switched the type of lot to a coffee shop and brought it back to a residential lot. The pop-up never showed up again, and my home was finally showing up after saving it.