There are some patterns in a duplicate question network that indicate that something is wrong and that the duplicate links should be fixed:
- a question is closed as a duplicate of a deleted question
- a question is closed as a duplicate of a question that is itself closed as a duplicate
- cyclic closing (though I don't think that is possible anymore)
- voting or answer length/amount disparity between duplicate source and target. For example, if the question closed as a duplicate has a higher voted and longer answer than the still open duplicate target, maybe the direction should be reversed.
Duplicates to deleted questions should be reviewed, as there might be a better duplicate target. If there isn't a better duplicate, the question should be reopened.
Duplicates of duplicates could be resolved automatically, and both questions should be made duplicates of the final element in the duplicate chain.
Cases of voting disparity in duplicates should also be reviewed and the best question and answer chosen as the canonical duplicate target.