Uh that usually happens to me when I close the browser and open the website again. It says I'm logged in, but I'm not.
To fix this I just press logout and login again. That's the reason it just says "Nickname" and doesn't show any characters.
Nope, this was an bug for like 3 hours xd. Even when I logged out it would do the same thing when I log back on. They resolved it now anyway.
It was addressed here. http://herowarz.koggames.com/2017/01...-issue-172017/
Note that it was not the black screen issue but the login issue.