Microsoft has completed work to resolve the issues affecting OneDrive for Business and SharePoint Online.
All affected services have been restored. Anyone still experiencing problems should contact the IT Support Centre.

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Previous Description (September 7, 2018 11:29):

Individuals using SharePoint Online features, including OneDrive for Business and Office Online may experience degraded performance, reduced functionality and/or receive error messages indicating that the server is unavailable.

Microsoft is currently investigating.

This notification will be updated when more information becomes available.