I also have this issue and it has destroyed the character and design of some of my skyscrapers and other builds.
Yes, this happens I my game as well. Also of note is that the wall trim will also disappear if there is a balcony above it. Not as bad as a problem, but it might irritate some people.
The only way to make it look better is to place plants like someone stated, or a window so that it looks like the break in the trim was intentional to allow for the window. However, the problem with that is that not only so you have to use bb.moveobjects on to place a window here, the upper portion of the window is nonfunctional from the inside. Trying to disguise this is also problematic as very few pictures cover the space. Here are a few pics to show what I mean:
@PugLove888 you should still be able to have exterior trim on that balcony as long as you have placed a flat above the ground floor in the balcony space. The game requires a level about ground level in order to apply the trim.