@loyabe Did you try demolishing the old building (maybe change it to residential at that point - something to make it completely different to the game's id of it), save and exit, then go in build mode and change the "Lot Type" for the lot to your desired lot type, save and exit the game, then re-enter to see if the lot type assigned stuck or not? Then load your new lot from the gallery/library and make sure the lot type is correct, then save and exit the game and go back in and see if the lot type stayed as your desired type?
If it were happening in my game I would try something like that whole process, then if it was still acting up I would start over but first remove all mods and cc, then run a game repair and do that whole process that I mentioned and see if it will stick.
Also, does this happen if you try in a fresh/new game?