Summary: A problem was noticed with the Plesk control panel related to a mariadb package. The package in question was updated which appears to have caused further updates. Both machines are being rolled back to their last snapshots (approx 3am) and will be back online around 09:30 this morning.
We’re keeping the original disks for analysis. We’ll ask Cloudlinux (the software vendor) to check them over to find out why they had this issue. This will be done prior to attempting to fix the packages again.
Update: 11:00: At 10:01 Plesk001 came back online. It had suffered file system corruption and has been restored to a new Disk. Plesk002 is back online without issue. This incident is considered closed.