In accordance with Heap’s data model, where users do events, each individual user in Heap is assigned a unique user ID, and each individual instance event is assigned a unique event ID.
On very rare occasions, the same event ID may be repeated for an instance of that event that was done by a different user. However, this will have no meaningful impact on your reporting.
There is an even smaller chance that you may see duplicates of the same event ID for the same user. No action is needed, as this, too, will have no meaningful impact on your reporting.