The server will be rebooted to complete the migration - this will take sites offline for a short period.
Downtime was kept within the estimated period, although delayed slightly due to the scale of the migration.
The work has been ongoing since 11pm last night, however there were some delays unfortunately caused by Cloudlinux licences not being activated immediately and some delayed responses from their support department, which delayed the migration start until 2am.
As such, the migration task overran, however didn't justify a restart of the entire process.
Sites will be online shortly, and services resumed (with the increased performance).
Please avoid contacting support / live chat whilst the process is completed.