@W11llf Not going to be many Unifi user's on the sky Forum, if i was you would just reset the gateway, stick it direct on the ONT and go from that point... Forget the SR203 all together, set the wan on DHCP iPv4 mode and see if it returns a wan IP to you.
Use the www.whatismyipaddress.com for it's return and if needed then sort out iPv6, search the forum XT8 and you will find a couple pictures to how an Asus is all setup, each Router has it's quirks so to speak!
Think someone posted on one off your multiples had it connected fine via a VF Hub so that would not be your case!
