We have guest users in our Azure AD. These guest users login with Microsoft account. Some of these accounts were disabled.
When a disabled guest user (blocked sign-in) tries to log into O 365, their browser goes into a redirect loop with multiple redirects between login.microsoftonline.com and login.live.com. After 7 or 8 redirects the user gets the error: Something went wrong and we can't sign you in right now. Please try again later.
The Microsoft account login server has detected too many repeated authentication attempts. Please wait a moment and try again.
I've seen it with my own MicrosoftID and various MS services, the usual solution is to clear the browser cache or use a private session. Or they just might have introduced a new regression, it's not like they spend a lot of time validating code nowadays... :)