I have a course with a couple of drag and drop interactions. They work well, but in both cases, the last item dropped disappears when the user moves to the next slide. It doesn't matter which item is dropped last, or where it is dropped, it disappears completely (not just behind the drop zone). If I go back to the slide, however, the item is in its proper dropped location. Any thoughts on what might be causing this? A scrubbed file is attached.