I'm back...
I just did this the other day BUT....
I have five photos. I am trying to create a collage using what I'll call the SWEEP and rotate out COLLAGE. It is in the first row of FIVE and it is the THIRD option on that row. I have the five photos on the timeline adjacent to each other. No matter whether I group the five together or leave them separate, when I apply that collage, only one photo is used in all five iterations.