Relayd not forwarding broadcast (BOOTP/DHCP) responses

Please. Read again. Try again. Ask when you are not sure.

Have you tried tcpdump on br-lan (or whatever your second interface is called)?
Have you seen matching DHCP packets on both interfaces (wlan0 vs br-lan)?

You have the tools to study the problem at its source, yet you keep guessing from side effects.
Does relayd do what it should be doing? Find that out first.

Good luck