My Deco XE75 Ethernet port 1 not working

Connecting internet into it will lead to a no internet red light.

Connecting a switch into it will lead to Deco online but any device connected to the swicth will be innacesible

Connecting a switch with the Secondary unit pluuged into it will crash my internet connection at all devices. If Secondary Deco is in either port 2 or 3 no issues

Any way to diagnose if port is no longer working? How to fix it?