Possible issue with spandrels.

I had the same problem while revisiting a Maxis building in StrangerVille. Like @Xinqun said, it was caused by friezes, and I wasn´t able to get a workaround without removing the friezes, what I didn´t want to. In the end I used trims to cover that particular part of a porch, and although it´s not the ideal solution, it now looks okayish.