I had the same issue, I tried in a different browser and it went through. There was a timeout error happening so it could be because of the types of settings you have for your browser.
is this on school wifi or work wifi by any chance? cause this usually means it is blocked
That's actually a cloudflare error, and that usually means the site was unreachable from that area for at least some period of time. However, I just checked by VPN to London, and the site seems reachable now, so it might have been an intermittent issue.
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On the Pre-Reg screen, when you submit your email the screen does say “thanks…”
But going back to that screen now, it's back to an entry box (to enter another email, ie for Alt accounts, etc).