A rule could fire twice if the event action occurs on a child element, but the selector in the condition is inclusive of both the child and parent. This behavior appears when the action triggers the rule to fire on the child element and then bubbles and fires again on the parent element.
To correct this behavior, deselect the 'allow events on child elements to bubble' option. Then check the 'don't allow if child element already triggers event' option within the rule. This change sets the rule to fire once per interaction.
More information on Troubleshooting Rules here: https://helpx.adobe.com/dtm/kb/Troubleshooting_Rule_Issues.html