I had actually done that. I had put a house on my lot with half walls, from the gallery, previous to this issue. And ever since, I had that problem with half walls. I just now went into the gallery and purchased a house with no half walls and went to the walls tool, and it basically fixed my issue. I can now transition from half walls to regular ones. I'm a newbie to Sims 4 so I bet it was my fault and I was just not realizing what I was doing, haha. But thank you so much for your help!