I encountered this review audit. To test me, the review item told me the question had received close votes as primarily opinion-based. This was obviously wrong, which I recognized quickly, but I saw a comment pointing to another question. It seemed like it might be a post might be a duplicate, so I opened the post in a separate tab, which revealed to me that the it was already closed as a duplicate--though of a different question than suggested in the comment.
(The question says it was closed as a duplicate by the Community ♦ bot, in case that's relevant. Since Community was listed as the sole close voter, I believe that simply means the question was closed after the OP confirmed to the system that they agreed with its duplicate status.)
At this point--since it was a Close Votes review item for a question that was already closed--I knew it was a review audit. I suspected this might be a new kind of review audit, where a highly upvoted but correctly closed duplicate would be used to test reviewers ability to select a reasonable close reason. I was pleased and intrigued at this possibility.
It also occurred to me that this might be a bug in the system, such that voting to close it as a duplicate of the question it's already duped to would make me fail the audit. But I figured there was only one (reasonable) way to find out, so I proceeded, and voted to close the question as a duplicate of what's already duped to. That is, in addition to correctly voting to close it as a duplicate, I also selected the correct duplicate.
Then the system told me I had failed the audit.
I believe this particular review-auditing behavior is both unintended and undesirable, and furthermore that it is not the result of errors made by Ask Ubuntu users in incorrectly closing questions (like some bad audits are) but instead is a design flaw in the system.
Either that, or I am missing something I should be noticing.
Note that this is not the result of a race condition: the post used for the audit was not closed between when the review item loaded and when I made my decision, but some days previously. (It was closed on March 30th and I reviewed it April 8th.)