The syntax of the path ... ntp server in config.boot.default is in the form of a leaf node with value instead of a tag node, even though it has always been a tag node as defined in XML.
This is normalized after load/save, and thus has gone unnoticed, but is not normalized by migration alone, which may lead to confusion or error if post-processing (say with cloud-init tools).
Make the change:
--- a/data/live-build-config/includes.chroot/opt/vyatta/etc/config.boot.default +++ b/data/live-build-config/includes.chroot/opt/vyatta/etc/config.boot.default @@ -29,9 +29,12 @@ system { address fe80::/10 address fc00::/7 } - server "time1.vyos.net" - server "time2.vyos.net" - server "time3.vyos.net" + server time1.vyos.net { + } + server time2.vyos.net { + } + server time3.vyos.net { + } } console { device ttyS0 {