A couple of weeks ago we identified that Forum posts are not being sent out to subscribers on certificates.moodle.com
I'm thinking it's Cron related, as Admin>Notifications is showing:
"The cron.php maintenance script has not been run for at least 24 hours."
This is vital because MCCC mentor-assessors use certificates.moodle.com to communicate regarding certificates, updates, exams, etc.
I did report this via firstname.lastname@example.org, so if there is already a Tracker item created it can be linked to here.