Managing personal Outlook.com account settings, security, and privacy
Found a solution! I had the same issue today, with that message showing up every 30 seconds;
Something went wrong and we can't sign you in at the moment. Please try again later. The Microsoft account login server has detected too many repeated authentication attempts. Please wait a moment and try again.
I'm using Microsoft Edge.
My solution was to refresh the page, block all the active cookies (by clicking on the lock icon next to the address bar), then to unblock them again (using the same lock icon - otherwise Outlook is not working anyways). Someone else mentioned the issue seemed related to cookies. It seems to be the case.