It looks like Getting 404 when closing a deleted question has resurfaced.
I don't have any screenshots, but the general steps to reproduce would appear to be:
- Open a question.
- Have someone else delete said question (or do it yourself from another session).
- Click "close" below the question.
At this point, you get a red "404" error box, as shown in this screenshot borrowed from the above-linked question:
The chain of duplicates on the above-linked question ends at Users without commenting privilege can't select the “it doesn't belong here” flag reason; a “404” error box appears when they try, which is status-completed. However, the fact that I got this same error about two months later would seem to indicate either a larger issue, that the questions indeed were not duplicates, or a regression.
Either way, I believe a developer should take a look at this.