OK, if you want to put the new ADSL router in place of the old one, just move the cabling (Internet cable comming from the splitter and going to the DSL port of the ADSL router) from the old ADSL...

Public IP address via default GW 0.0.0.0 in the routing table is normal. The other route 1.0.0.0/8 via WAN is the interesting one. Could it be from your attempt to add the 1.1.1.1 as a DNS ? Where do...

Do you have any equipment in the basement that activates between 1-4 am and may cause the interference that the technician mentioned as a probable cause ? For now lets see what would happen with the...

If you disable SmartConnect you would be able to use both bands (2.4 & 5 GHz).

@Woody Do you have any static routes added right now ? Please describe your configuration/cabling.

Apparently you have to reset to factory defaults and then reconfigure to overcome this issue - read through this thread.