Maintenance was carried out on the servers answering requests for the CMS Plugins on the weekend commencing 26/04 which included upgrading the OS of these machines.
As part of the upgrade of the operating system, the loopback adaptors configured with our Load Balancer IP addresses, which control the distribution of CMS plugin requests to the servers, were deleted.
Once this was identified by the SRE team at 9:29am the loopback adaptors were recreated and the issue was resolved at 9:39am. We will be updating our process documentation for upgrades to ensure that this is properly documented for any future maintenance.