Hello!
In current versions of VyOS relay-agents-packets in DHCP relay is dysfunctional due to misconfiguration.
If option is set, configuration script only add -m [value]to dhcrelay command:

if conf.exists('relay-agents-packets'):
    pkt = '-m ' + conf.return_value('relay-agents-packets')
    relay['options'].append(pkt)

(source)

But, this is not enough. According to Debian manual page, we also need to [[ https://manpages.debian.org/jessie/isc-dhcp-relay/dhcrelay.8.en.html#COMMAND_LINE | add -a key ]].

This is confirming also by dhcrelay source. Default value of add_agent_options is zero and can be changed only by -a key. And if add_agent_options is not 1, then whole add_relay_agent_options function, where performing processing of relayed packets with Relay Agent Information option, is skipped.

So, we need to add also -a option to command if relay-agents-packets is configured.