UPDATE:
Maintenance has ended, users with Skullgirls 2.1.1 can now login and play.
At the moment, this is ANDROID USERS ONLY as the App Store is still processing the 2.1.1 update.
iOS Users:
Upon launching the app, it will likely tell you to download a new version, but it won't be available in the App Store.
As soon as 2.1.1 is available for download in the App Store, you'll be able to play!
Android Users:
If you are experiencing login issues, or a black screen, please delete and reinstall the app!
So sorry for the confusion, everyone!