As this incident happened during our maintenance window, it allowed our sysadmin team to properly investigate the issue. It appears to be the same issue that affected montreal1000 earlier, which is a faulty kernal patch. This required our team to manually reboot the VM.
montreal300 cluster is now responding. More details once investigation is complete.
The data centre team continues to investigate to find the cause of what appears to be a network issue.
We're currently investigating an issue with the montreal300 cluster. More details here once available.