I've been having the same issue. None of the topics I'm following have been unfollowed, my email is the same yahoo email I've been using for 14 years or so (it's still very active), never changed my email for Kametsu, and the emails aren't in the junk folder. I noticed my very last new content email was June 1, which kind of coincides with IkarosBD's May 30 email update post previously linked above.
Kametsu probably thinks my active email is a disposable or inactive email. I don't visit the site everyday, so the email notifications are really important to me.