TL;DR: The registration popup for Discuss closes immediately and prevents registration for these forums.
I wanted to reply to an existing topic on the New Relic Discuss forum, but could not register for Discuss. I have an existing user for New Relic and I am logged in into the New Relic web app. When I select Help > Community I am presented a button where it says that I can proceed with with my existing account.
Then a popup would open and immediately close again, bringing me back to the New Relic Discuss page without logging me in. The same occurred also on a different machine (both Linux) and with different Browsers (Firefox, Chrome). I had to manually debug the process with Chrome dev tools to keep the window open. Turns out, this was the registration form for Discuss. Adding my details there and confirming the account finally logged me in, which is also the reason why I can post this message.