Same thing happening to me across newly built lots and premade buildings. I've attached a clip of mine below showing the stairs not being able to be deleted and the split level foundations bugging out/can't be deleted properly.
I know at some point mate54 is going to look into the stairs issues that quite a few people are having, maybe the foundations are causing them.
Edit: adding my google drive link that contains the Old Farm Road ZIP packaged lot from the attached clip, as well as another lot with this issue.
https://drive.google.com/drive/folders/1RQVfJgY5DE8DKwnRrxQNzNwfOTGGXGhw?usp=sharing