AX1800-R6700AX router issue

I just purchased this router to replace my still working old R6120 unit.

A soon as I connected it to my  network, it suggested a firmware update which I accepted. Once it was finally configured using same network and wls networks settings from my old router, I noticed that the Nighthawk web app will not show the attached devices at all. it just keep showing the "Please wait a moment" message", but it just hangs there. I even waited for 20 mins while I was doing something else. I ended switching to other settings without problems. I restarted the router twice with no change. it just cannot show the list of attached devices,

Any advice to make this router to work properly?