We experienced around six hours of forum downtime overnight (1.30am GMT to 7.30am 5th Nov 2020). During this time the forum was unavailable and login / registration for the site were also unavailable.
The error occurred due to an automatic upgrade of MairaDB which is incompatible with PHP 7.2 under certain configurations. Our database version has been rolled back (no data loss) until this is resolved. It looks like there will be a few sysadmins with headaches this morning from this!
We still believe the automatic upgrade policy is correct to ensure the system is patched and up to date, but we will be monitoring this.