In some cases, questions and answers that have been deleted are still showing up on
/review pages. They do not have "Improve" buttons, but they can still be approved or rejected. I'm not sure what causes a post to end up in this limbo state instead of being removed from the queue entirely, which I think is what's supposed to happen.
The suggested edit I noticed this on was here, but it just leads to a "Page Not Found" message now.
Tim Stone provided the following screenshot of another instance in chat: