The automated cPanel update process on November 5th has resulted in an issue with MariaDB (MySQL).
cPanel have provided advice on the following link:
For Shared Hosting and Managed Server customers, we are working through systems and downgrading MariaDB as they advise. If we have not yet reverted the update to your service will do so as soon as possible,.
If you are not a Shared Hosting customer or do not have a Managed Service, please follow the advice above if your web site(s) are currently down or affected by the issue.