The fix provided via https://github.com/vyos/vyos-1x/pull/4717 contained a nasty regression which was discovered during manual testing of VyOS 1.4.4.

The issue is in the migrator code where we do probe for dhcpv6 CLI node presence, but we probe for a CLI path and not a value of a CLI path.
https://github.com/vyos/vyos-1x/pull/4717/files#diff-24ce7b50bcb840419e741ffe1e180414e20b0485646c4ab9bffd9f9d03e1bc67R26-R28

In reality this instzead should be:

if config.exists(dhcpv6_addr_path) and 'dhcpv6' in config.return_values(dhcpv6_addr_path):
    autoconf_path = iface_base_path + ['ipv6', 'address', 'autoconf']
    if not config.exists(autoconf_path):
        config.set(autoconf_path)

on the downside - when working on VIF interfaces, we do only check https://github.com/vyos/vyos-1x/pull/4717/files#diff-24ce7b50bcb840419e741ffe1e180414e20b0485646c4ab9bffd9f9d03e1bc67R42-R44
and see if address CLI node is defined, but we do not check it's values, if DHCPv6 is used at all.