If a user has been archived or no longer has the same rights as before (after leaving the organization or changing positions), their actions become "orphaned", meaning they no longer have an assigned owner.
To identify orphaned ideas or actions, go to Action monitoring, use the "Owner" filter, click the two arrows to display more options, and select "Valid owner/ No".
Finally, click Search.
You can then simply reassign the action to a new owner, for example, by transferring the approver or changing the implementation coordinator.