Blog posts published before the MEE-1630 slug cleanup used URLs with consecutive hyphens, like /why-grief-advice-fails-when-your--0efc1d. After that release tightened slug validation, those old URLs stopped matching the redirect logic and started returning 404s — when they should have been sending visitors to the new canonical URL. Those redirects now work correctly.
A migration file numbering collision also caused the slug history table to silently skip creation on production. That table now exists where it should.