This has happened to me 4 times in the past hour, on two different machines. Both on normal posts and in what appear to be clearly audits.
When going through the "Low Quality Posts" queue, if I click 'Recommend Deletion' , I get a 404.
BEFORE:
AFTER:
If I click 'looks good' it works fine, although the only way I could prove it was by intentionally failing an audit: