Radius Authentication over SD-WAN

I have radius authentication working locally from the Sophos Firewall to the local radius server for both VPN and for WiFi authentication, however I am unable to get the authentication working from the Sophos Firewall to another radius server at a remote location over the SD-WAN link.

The SD-WAN link is working perfectly from any PC on the network and they can reach the remote Sophos Firewall, and anything on the remote network and vice-versa (including ping).  If I try to ping from the local Sophos Firewall to the remote network (Diagnostics page, or advanced console) I get 0 replies.

I have checked the configuration and both routing System-generated traffic and reply packets over the SD-WAN are enabled.

Any ideas on why I am not getting system generated traffic over the RED tunnel/SD-WAN?

Version: v20.2 Home - then updated to  v21 GA home

Thanks in advance

Ian