When accessing CAS, you are permitted a limited number of login attempts before your user name will be blocked.
This applies to every version of CAS, and includes the GB Cloud.
The login credentials include:
Your Sign-in Name
Your Sign-in Password
Your 2FA code (if implemented)
If you use LastPass or another online password storage utility, it may attempt to log you in automatically with an old 2FA. This will fail, and you'll exceed the threshold resulting in your IP being banned - without any effort on your part!
Failing to correctly enter all 3 credentials 5 times will result in a ban:
The resolution depends upon the server you are trying to access.