Just updating.
The issue seems to occur most often when I have three layers / floors and I use the highest floor. For example, offices on 1st floor, studio and dance on 2nd, doctor on 3rd. As long as I do not use the doctor on the third floor, I can send my singles through the offices, dance, and studio. The second I send one of my Idols to the doctor, I can no longer work on my singles at all.