It seems the Update process has reset all the wp_posts.comment_status fields on all my posts and pages to 'open'. Now I'm buried in post comment spam.
FWIW, I don't auto-expire posts because it also auto-expires pages so I run a batch job to expires posts (and not pages) that are older than x days. Re-running the batch job fixed this but only after getting buried in spam.
It would be good to separate the auto-expiration of posts from pages.