Hi @David Clarke ,
If a runbook activity returns multiple results the next runbook activity will be triggered that number of times (if you did not exclude something in a link).
So the next runbook activity will run that number of times, the flatten effects triggers the next runbook activities if the runbook activity has multiple results.
An runbook activity will produce a new set of data every time it runs, the flatten feature does not flatten data across multiple executions of the same runbook activity.
If you want that the next runbook activity will be triggered only once you also can put a Junction before that.
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Best regards,
Leon