Cue points and triggers, and another oddity

Your cue point triggers work just fine. Insert a shape on every slide layer and you'll see a difference. The problem is that objects on your base layer are visible on every slide layer and they don't appear B&W as they appear in the slide view. It does not work like that. I would use a some sort of semi-transparent shape as the slide layer background so objects on the base layer are not fully visible. Or even take a good screenshot of the base layer, turn it to a B&W version. I actually attached my version of your story file as a reference. I used a color image with B&W preset in picture format settings, and applied a screen blend mode with some light color. The second issue is a quick fix. Just unlock the slide layer visibility as shown in the attached screenshot. This option can be useful to hide or show a layer when you’re editing a slide or showing your other slide. If locked and visible on the base layer it will not show in preview.