That can be deleted since the network manager is supposed to spawn the other ifaces - if you like please read this thread DSLite Issues after upgrade to 4.0.1 - SW help - Turris forum where it is explained. See also the LuCI screenshot I posted as per your request.
If the network is up with the those ifaces (see LuCI screenshot) and the IPs assigned from the ISP then you should have ds-lite connectivity.
You could run from the cli check_connection to check whether ipv4|6 is working.
It would require more information to troubleshoot that, e.g. what is the systemlog printing in the event of connectivity loss.
You could also try adding option keepalive '6 10' to the config of the WAN iface.