Exact the same problem here. I can play Youtube but I can't play Netflix and NLziet anymore on my AVTex LG-WebOS-based SmartTV but I can on my iPhone which is connected to the same Wifi/mobile network trough the Rutx11. This happens after updating to RUTX_R_00.07.04.3 (both without or with erasing settings). Also RUTX_R_00.07.04.1 has the same issues. Netflix gives an error "Code NW-2-5" and NLziet starts the main menu but when I try to start a stream it wil never starts. Speedtest over the mobile connection in the Rutx is 88.3/42.5 with a latency of 26ms.
If I disable the mobile interface on the Rutx11 and connect to a WiFi hotspot on the Rutx11 everything works fine again (without editing any other settings). On older firmware versions of Rutx11 there were no problems with connecting to Netflix of NLZiet (in fact if I downgrade to RUTX_R_00.07.03.4 or lower everything works out of the box again.
I tried all kind of things with manual enter DNS servers (188.8.131.52 and 184.108.40.206) on the Ethernet interface, enter DHCP option6 for DNS server (and force them) but no luck at all.
The solution of changes on the CLI I am not really a fan of because most of the time these changes disappear with a firmware update or factory reset. I am pretty sure this undocumented 'feature' was added in the latest firmware versions.
I fact I am really disappointed about the Rutx at this point. Also the Wireguard (client) implementation is a pain in the butt. It's (Wireguard) a piece of cake on my Macbook and other (mobile) devices but on the Rutx it never really works.