According to your description, DHCPv6 relay agent can’t receive DHCP requests. We may check if the firewall on RRAS server has blocked the packet. If the firewall is on, we may turn off the firewall and test if it will work.
We may use network monitor on RRAS server, see if the NIC could receive solicitation packet.
If the NIC could receive, but GUI doesn't display, we may check the RRAS server’s configurations such as firewall setting as I have mentioned above. If even the NIC couldn’t receive, we may check the network connection between clients and DHCP relay agent. Verify if they are in the same subnet and check if the client could ping DHCP relay agent.
Hope this resolves your Query !!
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