I think it depends upon what needs to be done next with that work item.
If there is some work that needs to be done for that work item by a human, then it would be correct to mark the item as a business exception so that it can be reported out to a human to do whatever additional work is required that a robot could not do. If there is nothing else to be done for the item, then I think there is a valid reason for the case to be marked as completed (because all work is complete) but to tag the item to indicate the type of work it was (which will show on performance reports).
The word ""Exception"" should not be difficult for your RPA team to discuss or use. There should never be an expectation that the robots will be able to do 100% of work, they should be seen as a junior team able to work the majority of simple work, not mature cognative workers that will be able to work everything. This should be made clear to the business and your ROI calculations should have an expected exception rate built into it.