Maybe down for maintenance or something, when I registered my X670E crosshair hero last year around november/december it was working okay. I'm adding this info as I can see from looking at the dates of the posts this has happened in the past. Maybe contact support via the webform?
I thought I was alone in this. I have a motherboard, psu and LC II 360 that I wanted to register. The motherboard was successful but unfortunately, these two have failed. The submit button becomes unresponsive and nothing is happening, I have tried to clear the cookies and site data but no change.