People, especially developers, usually abhor duplication. But when running an EventStorming workshop, duplicating sticky notes is not necessarily evil, and even recommended.
Summary of the solution
The goal of an EventStorming workshop, whether you run a Big Picture, Process Modeling, or Software Design session, is to be as explicit as possible and enforce the timeline. So it is not a problem to see the same Event occur twice, three times or even more, on the design surface. It’s even recommended in order to gain clarity and avoid going back on the timeline.
Same goes for People, Systems, Aggregates and Policies. If they are involved at different moments in the process, then duplicate the sticky note to keep the timeline clean and enforce the flow.