I went to my WPMUDev Network Settings page today, and it prompted me to login. But the login page reloads without ever getting me back to the WPMUDEv dashboard properly.
I can login to the WPMUDev.org website, and my premium account is in good standing, so I thought I'd try an API key reset. No login. So I changed my password and tried login from my multisite with the new password, still no login. Interesting that if I use an incorrect password, your plugin tells me so, but when I use the correct password, the page refreshes and I am stuck at the "Let the Games Begin" login page.
I found a couple of threads related to cloud fare or SSL, but I use neither.