Ethernet - Router not assigning IP addresses to some devices.

Hi there, 

I have ATT Fiber, and everything was working fine until two days ago. Now two computers in my home (1 Mac and 1 Windows) will no longer connect via Ethernet and receive the error "Ethernet has a self-assigned IP address and will not be able to connect to the Internet." - both computers will connect wirelessly, but I need them connected via Ethernet for my work. 

Other wired devices to the network work fine, wireless is  the wall jack is working fine, the computers are fine (Contacted support for each after Customer Support told me it was an issue on my computer). 

When I first notified support I was sent a new router, but the problem persists. I asked if they could update router settings, but was told the connection was working fine and the issue was the ports on my computers. Both devices are brand new and working fine. Confirmed this is a router issue with both of my computer manufacturers yesterday. 

Each of the computers are connected via an internet switch, which was installed by the ATT Tech who installed the service. Service wires are about 5 months old as this is a new home. (Just trying to give all the details here) 

Steps taken to troubleshoot: 

New router installed

Renewed DHCP Lease 

Tested Wall Jack 

Tested other ethernet connect devices (working normally) 

Troubleshoot with both windows and mac tech team to verify devices are operating fine. 

*NOTE Computer will connect via Ethernet if manual IP address is entered, but need correct one to work properly 

Can someone tell me what settings in the router need to be adjusted to get these working via ethernet again?