Node 16, 17 and 19 are currently offline due to an unknown reason. We're awaiting an update from the data centre.
UPDATE @ 11:30 BST - All nodes have came back online. We're awaiting a response from the data centre as to a cause.
UPDATE: The cause was an uplink carrier in the data centre going offline, this caused re-convergence to occur which happened twice causing extended downtime up to 20 minutes.