Managing personal Outlook.com account settings, security, and privacy
Outlook is still going through a service disruption at the moment, so the issue you described may be related to this ongoing situation.
Below is a brief summary, and you can also track updates using this link: https://status.cloud.microsoft/
User impact: Users may experience intermittent issues signing in to Outlook.com.
Current status: We’ve received reports that impact associated with OL1292958 persists. We've resumed our investigation of the issue and are currently analyzing service telemetry and investigating reported behavior to determine scope and next steps.